C.J. Sniffen

Evaluation of a Mathematical Model of Rumen Digestion and an in Vitro Simulation of Rumen Proteolysis to Estimate the Rumen-Undegraded Nitrogen Content of Feedstuffs

Twelve grain mixtures, one lucerne (Medicago sativa) hay and one maize silage which had been used in mixed diets for which dietary nitrogen undegraded in the rumen (UDN) had been estimated with duodenally-cannulated cows, were studied. Total N in the feeds was fractionated into pool A (N soluble in borate-phosphate buffer), pool B (total N--(pool A + pool C)) and pool C (acid-detergent-insoluble N or residual N after 24 h incubation in protease solution). N solubilization in protease solution containing 6.6 units/ml (substrate-saturating enzyme concentration) indicated the presence of subfractions in pool B, with different rates of solubilization. Such subfractions were not detectable from in situ, Dacron bag, estimates of N solubilization. UDN was estimated using a dynamic mathematical model and rate-constants obtained from N solubilization in protease solution or in situ. For three grain mixtures tested using the protease technique the model predicted UDN values of 7, 10 and 12% compared with values of 47, 66 and 59% estimated in vivo. The full range of experimental feeds was tested using the in situ technique and UDN values predicted by the model were used to derive UDN values for twelve mixed diets. The latter values were significantly but not closely correlated with those determined in vivo (r2 0.41, P less than 0.05). An attempt was made to simulate rumen proteolysis in vitro by choosing a protease enzyme concentration (0.066 units/ml) providing a proteolytic activity similar to that of whole rumen fluid. The experimental samples of feed were subjected to simulated rumen proteolysis for 18 or 48 h to resemble the mean retention times in the rumen for grain mixtures and roughages respectively. The residual N at the end of incubation was considered as an estimate of UDN. The UDN values estimated from simulated rumen proteolysis and those determined in vivo for twelve mixed diets were in close agreement (r2 0.61, P less than 0.01). Simulated rumen proteolysis can serve as a simple, rapid and sensitive method to estimate UDN in a variety of feedstuffs.

Nutritional management of the pregnant dairy cow to optimize health, lactation and reproductive performance

Abstract The late gestation period is often viewed as a rest period between lactations. Management programs for the pregnant dry cow often reflect this view resulting in poor to marginal management and feeding programs being enacted. In contrast, current research suggests the concept of the late gestation period being a critical component to lactation preparation rather than an insignificant rest period between lactations. Required nutrient amounts for the dry pregnant cow are the sum of maintenance, pregnancy and reserve replenishment needs with additional requirements for growth during the first two pregnancies. Maintenance energy requirements can be dramatically increased by level of activity and adverse environmental conditions. A wide variety of feed ingredients can be successfully fed to dry cows as long as rations are appropriately formulated to meet energy, protein, mineral and vitamin requirements. Dry matter intake of the dry pregnant cow varies according to age, pregnancy status and time relative to calving. A substantial decline in intake occurs within the last 2–3 weeks of gestation for all age and pregnancy status groups supporting the need for a two diet dry cow program. Dietary concentration will need to be adjusted accordingly to ensure adequate nutrient intake to minimize potential metabolic disease during the peripartum period. The current model estimating energy requirement for pregnancy appears adequate in contrast to the protein requirement model. Research data would suggest that feeding additional protein in excess of the current requirement results in improvement of a variety of animal parameters critical to postpartum performance. The critical role of protein in the prepartum diet may be related to the role of amino acids providing for both fetal protein synthesis and a substantial amount of energy. A sound late pregnancy program results from integration of quality nutrition and cow management practices. Overall, a sound late pregnancy program is a critical key to improved lactating cow performance.

Refinement of an enzymatic method for estimating the theoretical degradability of proteins in feedstuffs for ruminants

Several enzymatic assays were examined to measure protein degradability. An alkaline protease from Streptomyces griseus (Type XIV) was used at pH 8 and pH 6.5, and a neutral protease from Bacillus subtilis was used at pH 6.5, a pH within the normal range of the rumen. Because many feedstuffs contain significant quantities of starch and occasionally β-glucans and pectins, a mixture of bacterial α-amylase and fungal β-glucanase (AFBG) was used to hydrolyse these components before the protease treatment. Using eight different feedstuffs (corn, wheat, barley, wheat bran, corn gluten meal, corn gluten feed, soybean meal and sunflower meal), comparisons with and without AFBG showed that the addition of AFBG significantly increased (P < 0.01) protein degradability by alkaline protease in starchy grains such as corn, wheat, wheat bran and barley. With the same 8 feedstuffs, the enzymatic methods (4 h incubation time) were then compared with in situ theoretical degradability using least squares linear fitting. The in vitro methods at pH 8 appeared to be the less predictive: they explained 61% and 68% of the variation in theoretical degradability for alkaline protease without and with AFBG, compared with 91% and 92% for experiments conducted at pH 6.5 for alkaline and neutral proteases with AFBG, respectively. No difference was observed on this basis in the measurement of protein degradability between the two enzymes at pH 6.5. Students t-test analysis of the regression equation slope and constant showed a small advantage for the alkaline protease method.

Improvement of the Streptomyces griseus method for degradable protein in ruminant feeds

Abstract The methods of Krishnamoorthy et al. [Krishnamoorthy, U., Sniffen, C.J., Stern, M.D., Van Soest, P.J., 1983. Evaluation of a mathematical model of rumen digestion and an in vitro simulation of rumen proteolysis to estimate the rumen undegraded nitrogen content of feedstuffs. Br. J. Nutr. 50, 555–568] and Roe et al. [Roe, M.B., Sniffen, C.J., Chase, L.E., 1990. Proc. Cornell Nutrition Conference, Dept. of Animal Science, Cornell University, Ithaca, NY, pp. 81–88], and a new one presented in this paper have been compared, and a revised procedure is proposed using a fixed ratio of enzyme to true protein (TP) determined by tungstic acid precipitation. A comparison of the three methods shows that they are statistically different. The ratio of enzyme has also significant effect ( p >0.01) on the estimate of degradable nitrogen when compared to the fixed concentration of enzyme in the original method. The effect of buffer pH (6.7 vs. 8) on degradation of protein sources was also statistically significant ( p >0.05) with somewhat higher degradation at pH 8.

Protein and amino acid nutrition of lactating dairy cattle.

This article describes the National Research Council Model of protein metabolism and illustrates its use in meeting the protein requirements of lactating cows. Attention is then directed toward amino acid nutrition with emphasis on the need for models to estimate amino acid requirements. Finally, the potential to improve productivity with rumen-protected amino acids is considered.

Protein and amino acid nutrition of lactating dairy cattle—today and tomorrow

Abstract The Cornell Net Carbohydrate and Protein System was used to (1) estimate absorbed amino acids provided by rumen escape protein and (2) formulate rations on the basis of amino acids. Forages, even those high in crude protein, only provide small amounts of rumen escape amino acids. Maize proteins are deficient in lysine. Oil seed proteins contain low levels of methionine. Animal and marine proteins, because of their high crude protein and low ruminal degradation, can be used to adjust the amino acid profile of absorbed protein, especially methionine (fish meal) and lysine (blood meal) Rations to support high levels of milk production need to contain protein sources with amino acid profiles that are complementary.

Estimation of the indigestible fiber in different forage types

The role of indigestible NDF is essential in relation to OM digestibility prediction, total tract digestibility, rumen fill, passage rate, and digestion kinetics. Moreover, the truly indigestible NDF (iNDF) represents a core point in dynamic models used for diet formulations. However, despite its wide possible applications, few trials have been conducted to quantify iNDF and even fewer to investigate whether or not it is consistent among different forage sources. The objective of this study was to predict the iNDF by measuring the residual NDF after 240-h in vitro fermentation to determine the unavailable NDF (uNDF) within and among various forage types. Finally, a mathematical approach was investigated for the estimation of the uNDF fraction. In all, 688 forages were analyzed in this study. This pool included 122 alfalfa hays, 282 corn silages, and 284 grass hays. Values of uNDF varied among different forages and within the same type (22.7% ± 4.48%, 20.1% ± 4.23%, and 11.8% ± 3.5% DM for grass hay, alfalfa hay, and corn silages, respectively). The relationship among uNDF and ADL was not constant and, for grass hay and corn silage, was different ( 0.05) from the 2.4 × lignin value applied by the traditional Chandler equation. The observed uNDF:ADL ratio was 3.22 for grass hay and 3.11 for corn silage. Relationships among chemical and biological parameters and uNDF were investigated via simple and multiple regression equations. The greatest correlation with a single variable was obtained by ADL and ADF when applied to the whole data set ( = 0.63). Greater coefficients of determination resulted from a multiple regression equation for the whole data set ( = 0.80) and within each forage type ( = 0.65, 0.77, and 0.54 for grass hay, alfalfa hay, and corn silage, respectively). In conclusion, a regression approach requires specific equations and different regression coefficients for each forage type. The direct measurement of uNDF represented the best approach to obtain an accurate prediction of the iNDF and to optimize its specific purpose in dynamic nutrition models.

Effect of corn silage hybrids differing in starch and neutral detergent fiber digestibility on lactation performance and total-tract nutrient digestibility by dairy cows.

Selection for hybrids with greater starch and NDF digestibility may be beneficial for dairy producers. The objective of this study was to determine the effect of feeding a TMR containing a floury-leafy corn silage hybrid (LFY) compared with a brown midrib corn silage hybrid (BMR) for intake, lactation performance, and total-tract nutrient digestibility in dairy cows. Ninety-six multiparous Holstein cows, 105±31d in milk at trial initiation, were stratified by DIM and randomly assigned to 12 pens of 8 cows each. Pens were randomly assigned to 1 of 2 treatments, BMR or LFY, in a completely randomized design; a 2-wk covariate period with cows fed a common diet followed by a 14-wk treatment period with cows fed their assigned treatment diet. Starch digestibilities, in situ, in vitro, and in vivo, were greater for LFY compared with BMR; the opposite was observed for NDF digestibility. Cows fed BMR consumed 1.7kg/d more dry matter than LFY. Although, actual-, energy-, and solids-corrected milk yields were greater for BMR than LFY, feed conversions (kg of milk or component-corrected milk per kg of DMI) did not differ. Fat-corrected milk and milk fat yield were similar, as milk fat content was greater for cows fed LFY (4.05%) than BMR (3.83%). Cows fed BMR had lower milk urea nitrogen concentration, but greater milk protein and lactose yields compared with LFY. Body weight change and condition score were unaffected by treatment. Total-tract starch digestibility was greater for cows fed the LFY corn silage; however, dry matter intake and milk and protein yields were greater for cows fed the BMR corn silage. Although total-tract starch digestibility was greater for cows fed the LFY corn silage, feed efficiency was not affected by hybrid type due to greater dry matter intake and milk and protein yields by cows fed the BMR corn silage.

Transition Cow Nutrition and Feeding Management for Disease Prevention

In this article, an overview is presented of nutrient modeling to define energy and protein requirements of the late pregnant cow, and metabolic relationships between fetus and cow as they relate to nutrient utilization and risk for postparturient disease are discussed. Recommendations for formulating dry cow diets are provided, with emphasis on opportunities to minimize variation and risk for postparturient disease events.

Grouping management and physical facilities.

Grouping management is one of the most important activities on the farm. It requires careful assessment of the daily routine on the farm and the development of a grouping/feeding management plan as well as a management plan that includes prioritization of the needed changes. If a good job is being done in this area, the cows will be more likely to respond to good nutrition.