The objectives of this experiment were to investigate the effects of two ruminally degradable protein (RDP) levels in diets containing similar ruminally undegradable protein (RUP) and metabolizable protein (MP) concentrations on ruminal fermentation, digestibility, and transfer of ruminal ammonia N into milk protein in dairy cows. Four ruminally and duodenally cannulated Holstein cows were allocated to two dietary treatments in a crossover design. The diets (adequate RDP [ARDP] and high RDP [HRDP]), had similar concentrations of RUP and MP, but differed in CP/RDP content. Ruminal ammonia was labeled with 15N and secretion of tracer in milk protein was determined for a period of 120 h. Ammonia concentration in the rumen tended to be greater (P = 0.06) with HRDP than with ARDP. Microbial N flow to the duodenum, ruminal digestibility of dietary nutrients, DMI, milk yield, fat content, and protein content and yield were not statistically different between diets. There was a tendency (P = 0.07) for increased urinary N excretion, and blood plasma and milk urea N concentrations were greater (P = 0.002 and P = 0.01, respectively) with HRDP compared with ARDP. Milk N efficiency was decreased (P = 0.01) by the HRDP diet. The cumulative secretion of ammonia 15N into milk protein, as a proportion of 15N dosed intraruminally, was greater (P = 0.003) with ARDP than with HRDP. The proportions of bacterial protein originating from ammonia N and milk protein originating from bacterial or ammonia N averaged 43, 61, and 26% and were not affected by diet. This experiment indicated that excess RDP in the diet of lactating dairy cows could not be efficiently utilized for microbial protein synthesis and was largely lost through urinary N excretion. At a similar MP supply, increased CP or RDP concentration of the diet would result in decreased efficiency of conversion of dietary N into milk protein and less efficient use of ruminal ammonia N for milk protein syntheses.

Effect of dietary crude protein level and degradability on ruminal fermentation and nitrogen utilization in lactating dairy cows.

Silage review: Mycotoxins in silage: Occurrence, effects, prevention, and mitigation.

Effect of rumen-protected methionine on feed intake, milk production, true milk protein concentration, and true milk protein yield, and the factors that influence these effects: a meta-analysis.

Impacts of the source and amount of crude protein on the intestinal supply of nitrogen fractions and performance of dairy cows.

In light of increasing global protein prices and with the need to reduce environmental impact of contemporary systems of milk production, the current review seeks to assess the feasibility of reducing levels of dietary CP in dairy cow diets. At CP levels between 140 and 220 g/kg DM there is a strong positive relationship between CP concentration and dry matter intake (DMI). However, such effects are modest and reductions in DMI when dietary CP is below 180 g/kg DM can be at least partially offset by improving the digestibility and amino acid profile of the undegradable protein (UDP) component of the diet or by increasing rumen fermentable energy. Level and balance of intestinally absorbable amino acids, in particular methionine and lysine, may become limiting at lower CP concentrations. In general the amino acid composition of microbial protein is superior to that of UDP, so that dietary strategies that aim to promote microbial protein synthesis in the rumen may go some way to correcting for amino acid imbalances in low CP diets. For example, reducing the level of NDF, while increasing the proportion of starch, can lead to improvements in nitrogen (N) utilisation as great as that achieved by reducing dietary CP to below 150 g/kg. A systematic review and meta-analysis of responses to rumen protected forms of methionine and lysine was conducted for early/mid lactation cows fed diets containing ⩽150 g CP/kg DM. This analysis revealed a small but significant (P=0.002) increase in milk protein yield when cows were supplemented with these rumen protected amino acids. Variation in milk and milk protein yield responses between studies was not random but due to differences in diet composition between studies. Cows fed low CP diets can respond to supplemental methionine and lysine so long as DMI is not limiting, metabolisable protein (MP) is not grossly deficient and other amino acids such as histidine and leucine do not become rate limiting. Whereas excess dietary protein can impair reproduction and can contribute to lameness, there is no evidence to indicate that reducing dietary CP levels to around 140 to 150 g CP/kg DM will have any detrimental effect on either cow fertility or health. Contemporary models that estimate MP requirements of dairy cows may require refinement and further validation in order to predict responses with low CP diets.

Reducing dietary protein in dairy cow diets: implications for nitrogen utilization, milk production, welfare and fertility.

Effects of Amounts and Degradability of Dietary Protein on Lactation, Nitrogen Utilization, and Excretion in Early Lactation Holstein Cows

https://www.genesisfeedproducts.com/wp-content/uploads/2015/03/choline_study.pdf

Supplementing limited methionine diets with rumen-protected methionine, betaine, and choline in early lactation Holstein cows.

The addition of cottonseed hulls to the starter and supplementation of live yeast or mannanoligosaccharide in the milk for young calves

Technical Note: Technique for Dissection and Analysis of the Rumen in Young Calves

Three studies were conducted to determine the potential of experimental feed additives (EFAs), clays or non-digestible yeast oligosaccharides, to reduce milk aflatoxin (AFM1) concentrations in lactating Holstein cows consuming aflatoxin-contaminated diets. All studies included a pre-treatment period and a 2-week experimental period in a randomized block design. During the pre-treatment period, cows received a total mixed ration (TMR) with no aflatoxin contamination. During both experimental weeks, all cows were fed a TMR containing aflatoxin-contaminated corn. During experimental week 1, cows received no EFA's in the TMR, but EFA's were included in the TMR for the second experimental week. In studies 1 and 2, the experimental period consisted of 2 weeks each lasting 7 days with 12 cows per treatment. Aflatoxin M1 concentrations were analysed by HPLC for milk samples collected on days 5-7 and days 11-14. In various experiments, treatments included control (no EFA), 100 g/cow daily of experimental Lallemand(®) product, 10 g/cow daily of MTB-100(®) -2004, (Alltech, Inc.), 10 g/cow daily of MTB-100(®) -2006, (Alltech, Inc.), 10 g/cow daily of experimental Alltech(®) product (Alltech, Inc.) and 227 g/cow daily of Astra-Ben 20(®) (AB-20(®) ; Prince Agri Products, Inc.). In study 3, the experimental period of 2 weeks each lasting 8 days and milk samples were collected from day 4 to 8 and day 11 to 16. Milk samples from study 3 were analysed for AFM1 concentrations by ELISA. For all experiments, changes in AFM1 concentrations because of the addition of EFA's were calculated. Four of the five EFAs tested in this study had no significant effect on AFM1 concentrations. However, the addition of AB-20(®) resulted in a significant decrease in AFM1 concentrations (60.4%). In summary, the addition of AB-20(®) to the diet of cattle appears to be effective for significantly reducing AFM1 concentrations in the milk of cows fed an aflatoxin-contaminated diet.

S. Davidson

Papers

Effects of Amounts and Degradability of Dietary Protein on Lactation, Nitrogen Utilization, and Excretion in Early Lactation Holstein Cows

Supplementing limited methionine diets with rumen-protected methionine, betaine, and choline in early lactation Holstein cows.

The addition of cottonseed hulls to the starter and supplementation of live yeast or mannanoligosaccharide in the milk for young calves

Technical Note: Technique for Dissection and Analysis of the Rumen in Young Calves

Effect of experimental feed additives on aflatoxin in milk of dairy cows fed aflatoxin-contaminated diets.