Showing papers in "Journal of Animal Science in 1983"
TL;DR: The need for a more integrated view of stress reactions in farm animals is emphasized and the respective role of each of these factors needs to be delineated more accurately.
Abstract: In animal husbandry, stress has usually been conceived as a reflex reaction that occurs ineluctably when animals are exposed to adverse environmental conditions, and which is the cause of many unfavorable consequences, ranging from discomfort to death. The inadequacy of this view is apparent from the new concepts that have been developed from research aimed at understanding the relationships between hormonal and behavioral reactions to stressful situations. Psychological aspects of environmental stimuli are powerful activators of endocrine responses. The amount of psychological stress that an animal experiences determines how much the pituitary-adrenal axis responds. Indeed, removing the variable of emotional arousal reduces or eliminates responses to some other stressors such as heat and cold. This means that one of the most important characteristics of the stress response, its nonspecificity, lies in the afferent part of the response, not the efferent. Hormonal and behavioral responses are intimately related in stressful situations. In particular, the perception and ensuing behavior of the subject are critical to the nature and intensity of hormonal response. Evidence from experiments in farm animals is presented to support these concepts. Because adjustment abilities are limited by genetics and previous experience, the respective role of each of these factors needs to be delineated more accurately. In addition, most experimental studies have been concerned with acute stress, while chronic multiple stress, which is more likely to be encountered in intensive husbandry, has received little attention. The approach in this field is hampered by the lack of suitable physiological criteria to assess long-term adaptive changes. Opportunities for further research are delineated and the need for a more integrated view of stress reactions in farm animals is emphasized.
451 citations
266 citations
TL;DR: Interactions between the conceptus and maternal systems are also responsible for initiating parturition, and these events are discussed, on a comparative basis, with respect to current knowledge obtained from studies of domestic farm animals and, where appropriate, data from laboratory species.
Abstract: The establishment and maintenance of pregnancy in domestic animals requires interactions between the developing conceptus and the maternal system. These interactions are essential for maintenance of the corpora lutea (CL), conceptus development and placentation, regulation of uterine endometrial secretory activity, placental transport of nutrients and gases, regulation of uterine blood flow, achievement of immunological "privilege" for the conceptus, stimulation of development of the maternal mammary glands and various other effects on the physiology and endocrinology of the maternal and conceptus systems. Interactions between the conceptus and maternal systems are also responsible for initiating parturition. All of these events are discussed, on a comparative basis, with respect to current knowledge obtained from studies of domestic farm animals and, where appropriate, data from laboratory species.
258 citations
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TL;DR: It is suggested that weaning pigs when younger than 5 wk old causes physiological changes detrimental to cellular immune reactivity that could alter disease susceptibility in young pigs.
Abstract: An experiment involving 118 pigs was conducted to evaluate the influence of weaning pigs at four different ages on in vivo and in vitro cell-mediated immunity. One-half of each litter was weaned at 2, 3, 4 or 5 wk of age; the other one-half remained with the sow as nonweaned controls. Phytohemagglutinin skin-test responses were determined on all pigs. Blastogenic responses of mitogen-stimulated lymphocyte cultures were determined before and after weaning. The intradermal response to phytohemagglutinin was reduced (P less than .001) in pigs weaned when 2 or 3 wk old and was suppressed (P less than .05) in those weaned when 4 wk old. In vivo cellular immunity was not altered by weaning in 5-wk-old pigs. The capability of lymphocytes to undergo blastogenesis in response to phytohemagglutinin was decreased in pigs weaned at 2 and 3 wk of age (P less than .001 and P less than .01, respectively). Pokeweed mitogen-stimulated blastogenesis was lower (P less than .01) in pigs weaned at 2 wk of age. Mitogen-stimulated lymphocyte blastogenesis was similar (P greater than .10) in control pigs and those weaned when 5 wk old. These data suggested that weaning pigs when younger than 5 wk old causes physiological changes detrimental to cellular immune reactivity. Those changes could alter disease susceptibility in young pigs.
183 citations
182 citations
TL;DR: Descriptive models of N metabolism have evolved that amalgamate current concepts and should prove useful in diet formulation to more fully utilize ruminal fermentation and increase productive efficiency of ruminant animals.
Abstract: Nitrogen metabolism of ruminant animals has been the subject of thousands of research publications. Study of ruminal and intestinal function continues. The quantitative and qualitative importance of ruminal microbes as a source of protein have become apparent in many trials, and factors controlling microbial protein synthesis or growth of microbes as well as ruminal degradation of dietary protein have been explored. Information on the supply side of the protein ledger (ruminal synthesis, bypass or escape of dietary protein; intestinal digestion) exceeds current knowledge of quantitative needs for amino acids. Descriptive models of N metabolism have evolved that amalgamate current concepts. With future amendments, these systems should prove useful in diet formulation to more fully utilize ruminal fermentation and increase productive efficiency of ruminant animals. Expanding knowledge of ruminal N metabolism will permit greater control and manipulation of the processes of ruminal fermentation and postruminal digestion.
155 citations
TL;DR: An experiment using 81 crossbred swine was conducted to evaluate quantitative and percentage chemical compositional changes of swine from 1.5 kg (birth) to 145 kg body weight, and foundLogarithmic and quadratic equations relating body composition to animal weight had similar R2 and lower coefficients of variation than linear or semilog functions.
Abstract: An experiment using 81 crossbred swine was conducted to evaluate quantitative and percentage chemical compositional changes of swine from 1.5 kg (birth) to 145 kg body weight. Groups of eight pigs were sacrificed at 1.5, 6.4 and 18 kg, and then at 18 kg increments to 145 kg. Body composition was determined by grinding the entire body, minus digesta, partitioning the carcass from other body components and chemically analyzing each subsample. Results indicated that weight of the carcass increased linearly with live weight, while the total weight of the other body components increased quadratically. Percentage fat in the empty body (ingesta-free) increased rapidly from birth to weaning (6.4 kg), plateaued until 36 kg and then increased, while water percentage declined dramatically from 1.5 to 6.4 kg, but then declined more gradually to 145 kg. Percentage protein increased from birth to 18 kg, plateaued and declined after 54 kg. When expressed on a fat-free basis, the percentage water decreased in a curvilinear manner with increasing animal weight while protein increased curvilinearly inverse to the change in water. Constancy of composition ("chemical maturity") between protein and water in the fat-free body was not attained by 145 kg. When expressed on an absolute empty body basis, water, protein and fat weight increased curvilinearly with increasing empty body weight; the rate of fat deposition increased faster during the latter growth stages while water and protein had declining deposition rates. Logarithmic and quadratic equations relating body composition to animal weight had similar R2 and lower coefficients of variation than linear or semilog functions. Gilts contained more water and less fat than barrows at similar slaughter weights, but sex differences were not apparent when expressed on a fat-free basis. The growth and fattening process was reflected in several carcass measurements. Backfat thickness, longissimus muscle area and body length increased as pig weight increased.
150 citations
TL;DR: Measured disappearance of dry matter and nitrogen from soybean meal suspended in dacron bags was lowest when the host animal was fed a high grain diet, while Disappearance of DM and N from SBM and distillers grains in rip-stop nylon bags was greater when these feedstuffs were in the pulverized form rather than in the commercially processed form.
Abstract: Four experiments were conducted to examine the effect of various factors on in situ digestion of feedstuffs in the rumen of Holstein cows. In Exp. 1, the effect of various days, animals and animal diets on in situ digestion was evaluated. Measured disappearance of dry matter (DM) and nitrogen (N) from soybean meal (SBM) suspended in dacron bags was lowest when the host animal was fed a high grain diet. No effect due to animals, day of incubation or period of experimentation was observed. The effect of bag porosity and substrate particle size on DM and N disappearance from bags was studied in Exp. 2. Rip-stop nylon, a material with small pores, appeared to decrease the influx of digesting agents into bags and limited efflux of digested residues from bags when compared with bags made from dacron polyester material. Disappearance of DM and N from SBM and distillers grains (DG) in rip-stop nylon bags was greater when these feedstuffs were in the pulverized form rather than in the commercially processed form. In Exp. 3, dacron and Acropore bags, with pore sizes of 52 and 5 microns, respectively, were used to examine DM and N disappearance, in the rumen of cows, from total mixed diets containing various dietary N sources. Lower DM and N disappearance from Acropore bags was observed for each of the diets regardless of time spent in the rumen; much of the difference was established within the first hour. The effect of formaldehyde treatment on degradation of amino acids from SBM suspended in dacron bags in the rumen for 16 h was studied in Exp. 4. Increased resistance of SBM amino acids to degradation in the rumen was observed as a result of formaldehyde treatment levels as low as .3% by weight. A possible increase in protection of lysine from degradation relative to other amino acids was also observed.
149 citations
TL;DR: It is concluded that ratio of concentration of estradiol in FF to both progesterone and androgens could be used to separate potential ovulatory (E-A) from atretic ( E-I) follicles in heifers.
Abstract: The objective of the present study was to characterize changes in growth, concentrations of steroids in follicular fluid (FF) and gonadotropin receptors of individual antral follicles after spontaneous luteolysis in heifers and to reexamine our hormonal method of classifying healthy and atretic follicles. Groups of heifers were ovariectomized (OVX) before regression of corpora lutea on d 17, 18 and 19 of an estrous cycle and after regression of corpora lutea at time periods before, during and after preovulatory gonadotropin surges. Each follicle greater than or equal to 6 mm in diameter was examined for concentration of progesterone, androstenedione, testosterone and estradiol-17 beta in FF and capacities of granulosal and thecal cells to specifically bind 125I-bovine follicle stimulating hormone (bFSH) or 125I-human chorionic gonadotropin (hCG). Follicles were separated into two classes, estrogen-active (E-A) or estrogen-inactive (E-I). Concentrations of estradiol in FF were higher than both progesterone and androgens in E-A follicles, whereas either androgens or progesterone was higher than estradiol in E-I follicles. Diameters, volumes of FF and numbers of granulosal cells in E-A follicles increased from d 17 through the end of the preovulatory gonadotropin surges. During this time, concentrations of progesterone, androstenedione and estradiol in FF and specific binding of 125I-hCG to granulosal and thecal cells increased, whereas specific binding of 125I-bFSH to granulosal cells decreased. In E-I follicles, progesterone in FF decreased and androstenedione increased from d 17 through end of gonadotropin surges. The E-I follicles had a higher incidence of granulosal cells with pycnosis than E-A follicles. We concluded that changes in growth, concentration of steroids in FF and gonadotropin receptors in E-A follicles after spontaneous luteolysis were similar to changes we previously reported for E-A follicles after prostaglandin-induced luteolysis, and that ratio of concentration of estradiol in FF to both progesterone and androgens could be used to separate potential ovulatory (E-A) from atretic (E-I) follicles in heifers.
TL;DR: In this paper, the effect of dietary level of vomitoxin-contaminated corn on performance and pathology was evaluated with young pigs to evaluate the effect on performance of young pigs.
Abstract: Summary Four trials were conducted with young pigs to evaluate the effect of dietary level of vomitoxin-contaminated corn on performance and pathology. A dietary level of approximately 20 ppm vomitoxin caused vomiting, 12 ppm vomitoxin caused almost complete feed refusal and 1.3 ppm caused a significant depression in feed intake and rate of gain. No lesions attributable to vomitoxin were observed in pigs fed up to 43 ppm dietary vomitoxin for a 21-d period. Alterations in various blood serum characteristics were observed in pigs fed vomitoxin, however, the effects could not be separated from those that may result from low intake of food.
TL;DR: Crossbred pigs used in three trials were assigned to one of three grouping treatments when moved to nursery pens and Combining alien pigs resulted in a significant increase in fighting but did not affect long term performance.
Abstract: Crossbred pigs (384) used in three trials were assigned to one of three grouping treatments when moved to 1.4 X 1.6 m nursery pens 4 h postweaning at 28 d of age. Treatments included eight pigs from the same litter (8-1), four pigs from each of two different litters (4-2) and one pig from each of eight different litters (1-8). A commercial odor masking agent (OMA) commonly used to reduce tail biting and fighting was sprayed on one-half of the replicates of each treatment 20 min after (trial 1) or immediately before (trials 2 and 3) the pigs were moved to the nursery. Agonistic behavior was quantified (trials 2 and 3) by direct observation for the first 3 h and again for 2 h at 24 and 48 h post-grouping. Application of OMA 20 min post-mixing caused only a temporary (3 to 5 min) cessation of fighting. A slight increase in fighting in all three grouping treatments was observed when OMA was applied before mixing. Average daily gain for 0 to 4 and 0 to 28 d and feed intake for 0 to 7 and 0 to 28 d were not influenced by OMA or grouping treatments. Combining alien pigs resulted in a significant increase in fighting but did not affect long term performance.
TL;DR: The high frequency discharges of LH between 12 and 20 wk are postulated to induce responsiveness of Leydig cells to LH and, thus, enable elevation of intratesticular testosterone to levels necessary for Sertoli cell differentiation and initiation of spermatogenesis.
Abstract: The temporal pattern of the endocrine changes associated with puberty were studied using 52 bulls born in October or April. Blood samples were taken weekly and at 30-min intervals for 5 h every 4-wk. Bulls were castrated at one of six 4-wk intervals between 12 and 32 wk and blood samples were taken. Season of birth affected concentrations of testosterone (greater for spring-born) in intact bulls, but not luteinizing hormone (LH) or follicle stimulating hormone (FSH). The concentration of FSH increased about 30% between 4 and 32 wk, without evidence of pulsatile discharge. Basal concentration of LH was low and pulsatile discharges were infrequent at 4 or 8 wk. At 12, 16 and 20 wk, however, basal LH concentration was elevated and LH discharges were at less than 2-h intervals. Testosterone concentration did not rise until 18 to 20 wk, but then continued to rise; LH discharge was suppressed concomitantly. Bulls castrated at 16 or 20 wk had higher concentrations of LH in their blood both before and shortly after castration values for bulls, but by 21 d after castration values for bulls of all ages were similar. It was concluded that elimination of an unidentified suppressive factor allows frequent discharges of LH between 12 an 16 wk, but the testes do not respond by secreting more testosterone until 18 to 20 wk. By 24 wk, the testes are secreting more testosterone and pituitary production of LH is restored to a lower level; LH discharges decline in frequency and basal LH level declines. The high frequency discharges of LH between 12 and 20 wk are postulated to induce responsiveness of Leydig cells to LH and, thus, enable elevation of intratesticular testosterone to levels necessary for Sertoli cell differentiation and initiation of spermatogenesis.
TL;DR: Feeding graded levels of each of the amino acids showed that the minimum lysine requirement for maximum growth was about 6.1% of protein, and the minimum arginine requirement was between 5.4 and 5.9% ofprotein, suggesting that the lysines requirements for prevention of fin erosion and mortality appeared to be lower than that for maximum weight gain.
Abstract: Triplicate lots of fry of rainbow trout (Salmo gairdneri) were fed a basal diet (47% protein) containing 67% corn gluten meal with and without a mixture of essential amino acids. The composition of the mixture was based on the differences between the amino acid contents of corn gluten meal and trout eggs. Fry fed the basal diet without added essential amino acids gained little weight, suffered high mortality and had eroded caudal fins. Addition of the mixture of amino acids (lysine, arginine, histidine, isoleucine, threonine, valine and tryptophan) significantly improved weight gain and prevented nearly all mortality and fin erosion. Single deletions of the amino acids valine, tryptophan, threonine, histidine and isoleucine had no significant effect on weight gain but the deletion of lysine alone significantly reduced weight gain and caused fin erosion and mortality. Deletion of arginine reduced weight gain (P less than .05), but did not cause mortality or fin erosion. Feeding graded levels of each of these two amino acids showed that the minimum lysine requirement for maximum growth was about 6.1% of protein, and the minimum arginine requirement was between 5.4 and 5.9% of protein. The lysine requirements for prevention of fin erosion and mortality appeared to be lower than that for maximum weight gain.
TL;DR: A review of the literature indicates heat stress generally causes lower milk production, decreased growth rate for cattle and lambs, but little effect on wool production.
Abstract: A review of the literature indicates heat stress generally causes lower milk production, decreased growth rate for cattle and lambs, but little effect on wool production. Breed and diet affects the degree of adverse response. Heat stress is caused primarily by high air temperature, but can be intensified by high humidity, thermal radiation and low air movement. Improving performance of animals under warm conditions involves breeding and management and modifying the environment. The former includes selection for heat tolerance, use of crossbred animals, diets with low heat increment in relation to energy for production and control of diseases and parasites. Environmental modifications may include provision of shades, use of water for evaporative cooling and increased air movement.
TL;DR: It is shown that in both nonparous and parous beef females, a large portion of the reproductive failure occurs by d 8 of gestation and would not have any noticeable influence on length of the estrous cycle.
Abstract: One hundred and two nonparous females, 18 to 24 mo old, and 55 parous or multiparous beef females, 3 to 12 yr old, were mated naturally (d 0) and slaughtered on d 2 to 5, 6 to 8 or 14 to 16 of gestation. Each reproductive tract was flushed with phosphate-buffered saline, and the flushings were searched for an oocyte or embryo. Parous females had a higher (P less than .05) fertilization rate than nonparous females. In nonparous females, reproductive failure was attributed equally to fertilization failure and embryonic mortality, which had occurred or was occurring by d 8 of gestation. In parous females, reproductive failure was attributed entirely to embryonic death. About 67% of this embryonic mortality had occurred or was occurring by d 8 of gestation; the other 33% occurred between d 8 and 16 of gestation. These findings show that in both nonparous and parous beef females, a large portion of the reproductive failure occurs by d 8 of gestation and would not have any noticeable influence on length of the estrous cycle.
TL;DR: Early weaned intact cows exhibited estrus 23 d sooner (P less than .05) than normally nursed cows, indicating there was no difference between the treatments for EW and NN without E2 but there was a large difference in the presence of E2.
Abstract: Twenty-three crossbred beef cows between 4 and 5 yr of age were assigned at random to one of six treatments: (1) ovariectomized 4 d postpartum (OVX) with early weaning of calves 21 d postpartum (OVX-EW; n = 4), (2) OVX-EW and 17 beta-estradiol implants (OVX-E2-EW; n = 4), (3) OVX and normal nursing by calves throughout the experiment (OVX-NN; n = 3), (4) OVX-NN and 17 beta-estradiol implants (OVX-E2-NN; n = 4), (5) intact cows and early weaning of calves 21 d postpartum (EW), (6) intact cows and normal nursed (NN). Blood was collected at 15-min intervals over a 4-h period once weekly during the 12-wk postpartum period in the OVX cows. Early weaned intact cows exhibited estrus 23 d sooner (P less than .05) than normally nursed cows. A hormone level for each cow at each week was determined from the mean of the 17 samples collected over the 4 h period each week. There were no significant changes due to E2 treatment, for concentrations of LH, FSH or number of pulses during wk 1 through 3. However, during wk 4 through 12 the linear and quadratic contrasts of wk X estrogen X nursing were significant for serum LH, indicating there was no difference between the treatments for EW and NN without E2 but there was a large difference in the presence of E2. During nursing E2 suppressed serum LH below that of nonestrogen-treated cows while after weaning E2 stimulated LH release above that of nonestrogen-treated cows.(ABSTRACT TRUNCATED AT 250 WORDS)
TL;DR: Diethylstilbestrol, at 1/70th of the oGH dose, was superior to oGH for improving FC, but did not alter average daily gain (ADG) or feed intake (ADF), and these observations do not support the concept that the mode of action of DES is through increased GH secretion.
Abstract: An 8-wk growth trial was conducted to assess the effects of ovine growth hormone (oGH; 7 mg/d, sc) on growth performance and carcass composition of normal, growing wether lambs. Diethylstilbestrol (DES; .1 mg/d, sc) and control lambs were included for comparisons. Plasma oGH levels at 8 wk were 1.9, 5.5 (P less than .05) and 138.1 ng/ml (P less than .001) for controls, DES and oGH lambs, respectively. Diethylstilbestrol did not increase plasma oGH until the fourth week. The oGH improved feed conversion 7.4% (FC; P less than .05), but did not alter average daily gain (ADG) or feed intake (ADF). Diethylstilbestrol increased ADG 15.3% (P less than .05) and improved FC 16.1% (P less than .01), with no effect on ADF. The primary effect of oGH on carcass composition was to decrease the quantity of fat 8.9% (P less than .05). In addition, oGH may have increased protein 6.5% (P less than .10) and moisture 4.0% (not significant). Diethylstilbestrol increased the quantity of carcass protein 10% (P less than .01) and moisture 8.7% (P less than .05), with no effect on fat. In these studies, the primary effect of exogenous oGH on normal, growing lambs was to reduce carcass fat, which may account for the observed improvement in FC. Diethylstilbestrol, at 1/70th of the oGH dose, was superior to oGH for improving FC (P less than .05) and ADG (P less than .10). Improvements in body weight of the lambs given DES were observed 2 wk before an increase in plasma oGH. In addition, DES, unlike exogenous oGH, did not alter the quantity of carcass fat. These observations do not support the concept that the mode of action of DES is through increased GH secretion.
TL;DR: Effects of photoperiod and plane of nutrition on growth, serum concentrations of prolactin (PRL) and growth hormone (GH) and puberty were assessed in Holstein heifers and body weight at puberty was recorded every month.
Abstract: Effects of photoperiod and plane of nutrition on growth, serum concentrations of prolactin (PRL) and growth hormone (GH) and puberty were assessed in Holstein heifers. Sixty pre-pubertal heifers were assigned to one of four treatment groups arranged in a 2 X 2 factorial. The two main effects were photoperiods of 8 h light: 16 h dark (8L:16D) vs 16L:8D, and a low vs high plane of nutrition. Heifers on the low plane of nutrition were fed a diet formulated to achieve a body growth rate of approximately .7 kg/d. Daily feed intake was restricted and similar in both groups of low plane heifers subjected to either 8 or 16 h of light daily. Heifers on the high plane of nutrition were fed ad libitum to achieve a growth rate greater than 1 kg/d. Body weight was recorded every month for 5 mo. The PRL and GH concentrations were measured at d 9, 53 and 132 in serum collected every 30 min for 6 h from five heifers in each treatment group. Progesterone was monitored biweekly in all heifers as an index of puberty (greater than 1 ng/ml). Heifers subjected to 8L:16D-low plane, 16L: 8D-low plane, 8L:16D-high plane or 16L:8D-high plane gained .61, .72, .98 and 1.08 kg/d, respectively. In the same treatment order, averaging across all bleedings, concentrations of PRL were 32, 37, 38 and 46 ng/ml serum, and GH averaged 10.9, 9.3, 9.8 and 9.0 ng/ml serum. Similarly, body weight at puberty averaged 268, 257, 278 and 268 kg, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
TL;DR: Much of the reduced productivity, and in particular the reduced nutritional efficiency, observed in ruminant production systems during the colder part of the year, can be accounted for by these adaptive changes.
Abstract: A review is presented of biological issues and practical consequences of the effects of cold stress on ruminant animals. When animals are subjected to extreme cold stress, substantial dietary energy may be diverted from productive functions to the generation of body heat. Failure to produce sufficient heat can result in death. More often, however, cold stress leads to the development of secondary changes and possibly disease. With prolonged exposure to even mildly cold conditions, physiological adaptation occurs in animals resulting in increases in thermal insulation, appetite and basal metabolic intensity, as well as alterations in digestive functions. Much of the reduced productivity, and in particular the reduced nutritional efficiency, observed in ruminant production systems during the colder part of the year, can be accounted for by these adaptive changes.
TL;DR: A lamb growth trial was conducted to evaluate soybean meal and blood meal and to compare two experimental designs (a completely randomized design and a switchback design); in both designs, there was a significantly greater conversion of protein to gain for blood meal (BM)-supplemented lambs than for Soybean meal (SBM)- supply-side lambs.
Abstract: A lamb growth trial was conducted to evaluate soybean meal and blood meal and to compare two experimental designs (a completely randomized design and a switchback design). A larger amount of variation was observed with the switchback than with the randomized design. A larger number of animals, longer treatment period or increased number of weighings may be needed to overcome end point weighing errors and decrease the variation in the switchback design. In both designs, there was a significantly greater conversion of protein to gain for blood meal (BM)-supplemented lambs than for soybean meal (SBM)-supplemented lambs. The relative value of BM compared with SBM was 251% (completely randomized design) or 296% (switchback design). Weighing steers 2 or 3 d at the beginning and end of the trial reduced variation and increased the probability of detecting differences in daily gain, gain/feed and protein efficiency when compared with a standard weighing method (once at the beginning and once at the end of the trial). Regressing 11 weekly weights on an average of one, two or three initial and final weights also reduced variation and increased the probability of detecting treatment differences. Regressions of weekly weights were more useful as the number of initial and final weights was decreased. Daily gain and gain/feed increased linearly (P less than .05) with protein level when BM or SBM was fed. A nonlinear model was used to predict protein requirement, maximum gain and relative protein values. There was a range in relative values for BM of 255 to 348% depending on the method of analysis used.
TL;DR: The effects of a single injection of testosterone propionate on concentrations of follicle-stimulating hormone (FSH) during diestrus, and to relate the normal and perturbed patterns of FSH secretion to subsequent estrous characteristics and fertility were investigated in this article.
Abstract: Twelve mares fed altrenogest for 14 d were used to study the effects of a single injection of testosterone propionate on concentrations of follicle-stimulating hormone (FSH) during diestrus, and to relate the normal and perturbed patterns of FSH secretion to subsequent estrous characteristics and fertility. Seven of 12 mares received testosterone propionate at 200 micrograms/kg of body weight on d 5 of progestogen feeding. Mares were teased and blood samples were drawn daily; all mares were artificially inseminated at the first estrus after progestogen treatment. Testosterone propionate treatment caused a 50% reduction in concentration of FSH in plasma within 24 h, and this effect persisted through 48 h after injection. Within 4 d after the suppression of FSH secretion, concentrations of FSH rebounded and were significantly elevated compared with control values during the last 4 d of progestogen feeding. Testosterone propionate at this dosage also elicited estrous behavior in five of seven treated mares within 24 h after injection. After withdrawal of progestogen feeding, the interval to onset of estrus, duration of estrus, and magnitude of the luteinizing hormone peak were similar between groups (P greater than .05). Six of seven treated mares and three of five control mares became pregnant to breeding on the first estrus after progestogen treatment. Because manipulation of the normal pattern of FSH secretion during diestrus did not affect estrous characteristics or fertility of the subsequent estrus, such treatment may have potential as a means of synchronizing FSH surges during diestrus in the mare.