Undesirable side effects of selection for high production efficiency in farm animals: a review

Life history theory provides a metatheoretical framework for the study of pubertal timing from an evolutionary-developmental perspective. The current article reviews 5 middle-level theories--energetics theory stress-suppression theory psychosocial acceleration theory paternal investment theory and child development theory--each of which applies the basic assumptions of life history theory to the question of environmental influences on timing of puberty in girls. These theories converge in their conceptualization of pubertal timing as responsive to ecological conditions but diverge in their conceptualization of: a. the nature extent and direction of environmental influences and; b. the effects of pubertal timing on other reproductive variables. Comparing hypotheses derived from the 5 perspectives are evaluated. An extension of W.T. Boyce and B.J. Elliss (in press) theory of stress reactivity is proposed to account for both inhibiting and accelerating effects of psychosocial stress on timing of pubertal development. This review highlights the multiplicity of (often unrecognized) perspectives guiding research raises challenges to virtually all of these and presents an alternative framework in an effort to move research forward in this arena of multidisciplinary inquiry. (authors)

https://cals.arizona.edu/fcs/sites/cals.arizona.edu.fcs/files/Psyc%20Bull%20Ellis%202004.pdf

Timing of Pubertal Maturation in Girls: An Integrated Life History Approach.

Leptin, a 16-kDa protein secreted from white adipocytes, has been implicated in the regulation of food intake, energy expenditure, and whole-body energy balance in rodents and humans. The gene encoding leptin was identified by positional cloning and is the mutation leading to the profound obese phenotype of the ob/ob mouse. Exogenous administration of leptin to ob/ob mice leads to a significant improvement in reproductive and endocrine status as well as reduced food intake and weight loss. The expression and secretion of leptin is highly correlated with body fat mass and adipocyte size. Cortisol and insulin are potent stimulators of leptin expression, and expression is attenuated by beta-adrenergic agonists, cAMP, and thiazolidinediones. The role of other hormones and growth factors in the regulation of leptin expression and secretion is emerging. Leptin circulates specifically bound to proteins in serum, which may regulate its half-life and biological activity. Isoforms of the leptin receptor, members of the interleukin-6 cytokine family of receptors, are found in multiple tissues, including the brain. Many of leptin's effects on food intake and energy expenditure are thought to be mediated centrally via neurotransmitters such as neuropeptide Y. Multiple peripheral effects of leptin have also been recently described, including the regulation of insulin secretion by pancreatic beta cells and regulation of insulin action and energy metabolism in adipocytes and skeletal muscle. Leptin is thought to be a metabolic signal that regulates nutritional status effects on reproductive function. Leptin also plays a major role in hematopoeisis and in the anorexia accompanying an acute cytokine challenge. The profound effects of leptin on regulating body energy balance make it a prime candidate for drug therapies for humans and animals.

The biology of leptin: a review.

Nematode Parasites of Vertebrates: Their Development and Transmission

Metabolic fuels and reproduction in female mammals.

Prolificacy has been defined as the number of viable piglets produced per year or per breeding lifetime. Prolificacy is influenced by age at first successful mating, ovulation rate and embryo survival at each mating, number of live born, viable pigs and the sow's ability to be successfully remated at regular intervals. It is concluded that under normal conditions of feeding and management nutrition will have a minimal influence on gilt prolificacy. However, to gain the advantages of a slightly younger age at puberty, maximal ovulation rate and an adequate fat cover (if only to ensure against subsequent poor management), gilts should be fed ad libitum up to the time of mating. Long-term performance is best served by minimizing fluctuations in live weight and fat reserves, so avoiding extremes of body condition and subsequent poor performance. This is achieved by small controlled increases in sow body weight during pregnancy and feeding to appetite for restricted periods each day during lactation. Assuming the sow has not achieved a very poor condition during lactation, feeding level during pregnancy will have little effect on numbers of piglets born, and only a limited influence on piglet birthweights. The conclusion that piglet birth weights will be influenced more by total pregnancy feed intake than pattern of feed distribution is unchallenged. Lactation feed intake is shown to have marked effects on the post-weaning performance, low-level feeding leading to an extension of the remating interval and possibly increasing embryo mortality. No benefit of high-level feeding after weaning is demonstrable, except possibly in primiparous sows or sows having suffered an extreme loss of liveweight and body condition during the previous lactation.

Nutrition and sow prolificacy.

The relationship between age, live weight, body composition and energy status on the onset and maintenance of reproductive activity in females is reviewed. When possible, swine studies have been employed, although, of necessity, much data are drawn from other species. The relationship between age, weight and puberty is controversial. However, from the available data we conclude that neither age nor weight are reliable indices of reproductive development, but that minimum threshold values for these characteristics must be achieved before puberty can occur. Human data provides a strong indication that a minimum adipose to lean tissue ratio is a prerequisite for puberty onset. Limited data from swine support this contention and indeed it may be a superior measure of reproductive development than either age or weight. However, the value of this ratio remains to be defined in pigs, and again it is minimum threshold level, the attainment of which is necessary, but not in itself sufficient, for puberty onset. A positive energy balance seems to be necessary for puberty onset and the maintenance of estrous cycles in some species, but this has not been investigated in swine. The mechanisms whereby adiposity and energy status influences reproduction are discussed. Human studies demonstrate a negative correlation between energy status, body fatness and plasma gonadotrophin levels. Also, adipose tissue has the ability to metabolize sex steroids, aromatizing androgens to estrogens and changing the direction of estrogen metabolism to produce more or less biologically potent estrogens.

Energy intake, body composition and reproductive performance of the gilt.

Lipid profiles of sperm and seminal plasma from boars having normal or low sperm motility

To study the effects of feed intake during lactation and after weaning on reproductive performance, 89 second-parity Lacombe sows were allowed 6 kg feed d−1 (H) or were restricted to 3 kg feed d−1 (R) during lactation and during the weaning to estrus interval (WEI); this resulted in a 2 × 2 factorial design (groups HH, HR, RH and RR). To minimize the confounding effects of duration of WEI on sow performance, the experiment was terminated 10 d after weaning. The diet was formulated to provide 12.4 M J ME kg−1 and 16% crude protein. Restricted feeding during lactation resulted in a longer (P < 0.05) WEI (7.3 d vs. 5.9 d). WEI was not affected by feed intake after weaning. Fewer (P < 0.05) sows feed restricted during lactation exhibited estrus by 10 d from weaning (31.8% vs. 88.9%). Ovulation rate was not affected by lactation or postweaning feed intake. However, embryo survival at 25 d of gestation was influenced (P < 0.05) by feed intake during both periods. The highest embryo survival (85%) was in HR sows...

Effect of feed intake during lactation and after weaning on sow reproductive performance

Two experiments were performed with 78 second parity Lacombe sows to determine the influence of nutrition on reproductive performance. During a lactation of 35 d sows were fed daily either 3 (L) or 6 kg (H) of a diet having 16% crude protein and 12.5 MJ DE kg−1. For exp. 1, six L- and six H-fed sows were given an intravenous injection of gonadotropin releasing hormone (GnRH) at 21 d of lactation and blood was sampled at −30, −10, 0, 10, 20, 30, 45, 90 and 120 min from the time of injection. Prestimulation luteinizing hormone (LH) levels were lower for L-fed than for the H-fed sows (1.34 ± 0.1 vs. 1.93 ± 0.2 ng mL−1' P < 0.02). Peak LH levels achieved after UnKH injection, however, did not differ significantly (5.0 ± 0.6 and 5.8 ± 0.5 ng mL−1 for L and H sows, respectively). In exp. 2, 38 sows were fed the H and 40 fed the L level of feed throughout a 5-wk lactation. As expected, low-level feeding in lactation resulted in a greater body weight and backfat loss (17.4 ± 1.6 vs 41.2 ± 2.3 kg and 3.2 ± 0.4 vs....

Roy N. Kirkwood

Papers

Nutrition and sow prolificacy.

Energy intake, body composition and reproductive performance of the gilt.

Lipid profiles of sperm and seminal plasma from boars having normal or low sperm motility

Effect of feed intake during lactation and after weaning on sow reproductive performance

The influence of feeding level during lactation on the occurrence and endocrinology of the postweaning estrus in sows