Effect of yeast supplementation on performance, rumination time, and rumen pH of dairy cows in commercial farm environments.

The aims of the present study were to evaluate the effects of live yeast supplementation (Vistacell MUCL 39855, AB Vista, Marlborough, UK) on performance, rumination time, and rumen pH on dairy cows in commercial farm environments. Three trials were carried out, the trials lasted 12 (trial 1), 15 (trial 2), and 19 wk (trial 3). In each trial, 14 multiparous Holstein dairy cows were allocated to 2 groups that received (trial 1) a standard diet plus yeast, (trial 2) an acidogenic diet plus yeast, and (trial 3) grazing pasture plus yeast. Milk production, milk chemical characteristics, body weight and body condition score, rumination time, and rumen pH were monitored for each group throughout the 3 trials. No statistically significant differences were observed in any of the 3 trials for any of the recorded variables. In contrast, an effect of time (period or days in milk) on rumen pH was observed in all 3 of the trials, as time spent under the acidotic thresholds increased across the experimental periods; however the differences were not associated with live yeast supplementation. No effect of live yeast supplementation was observed in any of the 3 trials reported. Further research should include studies on animals at different stages of lactation (with emphasis on transition period and early lactation), consuming more challenging diets (higher level of inclusion of concentrates or starch), or under different environments such as grazing of succulent forages. Such studies might be required to elucidate any possible effect of live yeast supplementation of dairy cows when the rumen environment is under challenge.

Comparison of rumination activity measured using rumination collars against direct visual observations and analysis of video recordings of dairy cows in commercial farm environments.

Automated systems for monitoring the behavior of cows have become increasingly important for management routines and for monitoring health and welfare. In the past few decades, various devices that record rumination have been developed. The aim of the present study was to compare rumination activity measured with a commercially available rumination collar (RC) against that obtained by direct visual observations and analysis of video recordings in commercial dairy cows. Rumination time from video recordings was recorded by a trained observer. To assess observer reliability, data were recorded twice, and the duration of recorded behaviors was very similar and highly correlated between these 2 measurements (mean=39±4 and 38±4 min/2 h). Measurements of rumination time obtained with RC when compared with analysis of video recordings and direct observations were variable: RC output was significantly positively related to observed rumination activity when dealing with animals housed indoors (trial 1 video recordings: slope=1.02, 95% CI=0.92-1.12), and the limits of agreement method (LoA) showed differences (in min per 2-h block) to be within -26.92 lower and 24.27 upper limits. Trial 1 direct observations: slope=1.08, 95% CI=0.62-1.55, and the LoA showed differences to be within -28.54 lower and 21.98 upper limits. Trial 2: slope=0.93, 95% CI=0.64-1.23, and the LoA showed differences to be within -32.56 lower and 19.84 upper limits. However, the results were poor when cows were outside grazing grass (trial 3: slope=0.57, 95% CI=0.13-1.02, and the LoA showed differences to be within wider limits -51.16 lower and 53.02 upper). Our results suggest that RC can determine rumination activity and are an alternative to visual observations when animals are housed indoors. However, they are not an alternative to direct observations with grazing animals on pasture and its use is not advisable until further research and validation are carried out.

Nutrient partitioning between reproductive and immune functions in animals.

The physiological processes that underlie the reproductive cycle impose considerable metabolisable protein (MP) demands on a female, especially during the periparturient period. When MP supply falls short of MP demand (i.e. MP becomes scarce), certain, if not all, bodily functions are expected to be penalised. It has been proposed that partitioning of scarce MP is prioritised to reproductive rather than to immune functions. In other words, at times of MP scarcity, the penalty on expression of immunity would be expected to be greater than that on reproduction. This hypothesis forms a nutritional basis for the occurrence of periparturient breakdown of immunity to parasites (BIP), which can be observed in many host-parasite systems. In the present review we explore this nutritional basis, using periparturient sheep infected with the abomasal nematode Teladorsagia circumcincta as an example, and attempt to quantify its occurrence. Evidence supporting the nutritional basis of periparturient BIP is reviewed, covering experiments in which nutrient supply (from both exogenous and endogenous sources) and/or nutrient demand were manipulated. Quantitatively, MP requirements for expression of immunity to T. circumcincta were estimated to be about 1 g/kg metabolic body weight (body weight 0.75) per d, approximately 5% of the maximum MP requirements of periparturient sheep. The major component of this requirement was assumed to be for replenishing irreversible plasma protein losses into the gastrointestinal tract. Although confirmation of this estimate is required, such estimates may be used to improve the known MP requirements of periparturient animals, enabling the extent and the consequences of periparturient BIP to be minimised.

Metabolic constraints on voluntary intake in ruminants.

The weak point in all current methods or models of diet formulation is the prediction of intake. The major uncertainty is not in the cases in which physical constraints apply, but in those in which voluntary intake is limited by feedback from metabolic factors. Voluntary intake is, ultimately, a psychological phenomenon, involving the integration of many signals, and reflects the flexibility of biological systems evolved to cope with variability in food supply, composition and animal state. Conditions giving rise to regulatory signals may provide a framework for modeling metabolic constraints on intake. The empirical evidence for metabolic feedback shows that the animal's productive potential, which affects its ability to utilize nutrients, interacts with the balance of absorbed nutrients to regulate intake. The relative importance of the sites where nutrient imbalance occurs (microbial or host animal metabolism) is unclear, as is the relevant time scale (minutes or days) of response. A model of the effects of asynchrony of nutrient supply to ruminal microbes suggests that ammonia and microbial recycling and the contribution of hind-gut fermentation reduce the asynchrony in the balance of nutrients absorbed into the bloodstream. Hitherto, rather little progress has been made in mathematical modeling of the metabolic processes controlling intake. Models that describe the phenomenon in terms of global variables, such as total energy intake, protein supply, and protein synthetic capacity, can simulate the way constraints may operate without requiring or providing a deeper understanding of the metabolic processes involved. Models describing the flux of energy and materials down established metabolic pathways have the potential to explore constraints on intake, but until the problem of parameterizing such models can be overcome, that potential will remain untapped.

Mammary sensitivity to protein restriction and re-alimentation.

The present study tested the influence of protein undernutrition and re-alimentation on mammary gland size and secretory cell activity in lactating rats. During gestation, female Sprague-Dawley rats were offered a high-protein diet (215 g crude protein (N x 6.25; CP)/kg DM; H); litters were standardized to twelve pups at parturition. During lactation, two diets were offered ad libitum, diet H and a low-protein diet (90 g CP/kg DM; L). Lactational dietary treatments were the supply ad libitum of either diet H (HHH) or diet L (LLL) for the first 12 d of lactation, or diet L transferring to diet H on either day 6 (LHH) or 9 (LLH) of lactation. On days 1, 6, 9 and 12 of lactation, rats from each group (n > or = 6) were used to estimate mammary dry mass, fat, protein, DNA and RNA; the activities of lactose synthetase (EC 2.4.1.22) enzyme and Na+,K(+)-ATPase (EC 3.6.1.37) were also measured. Rats offered a diet considered protein sufficient (H) from day 1 of lactation showed a decrease in mammary dry mass and fat but an increase in DNA, RNA and protein on day 6, after which there was no further change, except for mammary protein which continued to increase. However, rats offered diet L showed a steady loss in mammary mass and fat throughout the 12 d lactation period and no change in mammary DNA, RNA or protein. Rats previously protein restricted for either the first 6 or 9 d of lactation had their mammary dry mass and mammary fat loss halted and showed a rapid increase in mammary DNA, RNA and protein on re-alimentation. Lactose production in group HHH, as measured by lactose synthetase activity, was similar on days 1 and 6 of lactation, after which a significant increase was seen. Protein-restricted rats showed no change in lactose synthetase activity during the 12 d experimental period. Changing from diet L to diet H led to a significant increase in lactose synthetase activity to levels comparable with those offered diet H from day 1. These results show that rats offered a protein-restricted diet during lactation suffer mammary underdevelopment, but this may be rapidly reversed by re-alimentation with a high-protein diet.

Modeling metabolic costs of allelochemical ingestion by foraging herbivores.

A mathematical model of intermediary metabolism of allelochemicals by vertebrate herbivores is presented and used to quantify the metabolic costs of detoxification. Conjugation with glucuronic acid and maintenance of acid-base status causes catabolism of amino acid and is shown to result in loss of body protein and depletion of glucose. An interaction between allelochemical dose and nutrient status is found, and the ratio of allelochemical to nutrient absorption rate defines the tolerance of the animal to absorbable allelochemical concentration in foods. The interaction is nonlinear and the ecological implications of this for foraging behavior and diet choice are discussed.

Maternal protein reserves and their influence on lactational performance in rats. 4. Tissue protein synthesis and turnover associated with mobilization of maternal protein.

The present study was undertaken to investigate the changes in muscle protein turnover involved in the rapid mobilization of protein in rats subjected to severe protein restriction during lactation. Estimates of mammary gland and liver protein synthesis were also made during lactation. Multiparous female Sprague-Dawley rats, caged individually following mating, were offered a high-protein diet (H; 215 g crude protein (N x 6.25; CP)/kg dry matter (DM)) ad lib. until parturition. Following parturition, half the females continued to receive diet H, whilst the remainder were offered a diet low in protein (L; 90 g CP/kg DM) ad lib. On days 2, 4, 8 and 12 of lactation, groups of females were used in the estimation of tissue protein synthesis (flooding dose of [3H]phenylalanine) immediately after a milk sample had been obtained. Rates of muscle protein synthesis were unchanged during lactation in group H. The feeding of diet L during lactation reduced the muscle protein synthesis on day 12 to rates that were lower than group H and also the rate on diet L on day 2 (P < 0.01). However, this fall in muscle protein synthesis was not rapid and muscle fractional synthesis rate (FSR) was different from group H only from day 8 (P < 0.05). Estimated rates of mammary protein synthesis appeared to be generally unchanged by dietary treatment or stage of lactation. Liver FSR was also unchanged by dietary protein supply or stage of lactation. The effect of dietary protein restriction on liver size and protein content during lactation influenced liver absolute synthesis rate (ASR), and on days 8 and 12 of lactation liver ASR was lower in group L than in group H (P < 0.001). The loss of muscle protein in rats fed on diet L during lactation (133 mg) occurred mainly between days 2 and 8 of lactation and was primarily associated with a dramatic increase in degradation (13.0% per d), with the decline in synthesis having a much smaller role. A decline in muscle protein degradation during the latter half of lactation was part of the mechanism that prevented excessive muscle protein catabolism. It is thought that the estimation of mammary protein synthesis in the present study was impaired by the milk sampling procedure previously used.

Maternal protein reserves and their influence on lactational performance in rats. 3. The effects of dietary protein restriction and stage of lactation on milk composition.

The effects of severe protein restriction following parturition on the changes in rat milk composition during lactation were investigated using multiparous female Sprague-Dawley rats caged individually following mating and offered a high-protein diet (H; 215 g crude protein (N x 6.25; CP)/kg dry matter (DM)) ad lib. until parturition. Following parturition, half the females continued to receive diet H, whilst the remainder were offered a diet low in protein (L; 90 g CP/kg DM) ad lib. On days 2, 4, 8 and 12 of lactation groups of females from both dietary treatments were used to provide a milk sample. Milk samples were analysed for their lactose (enzymically), protein (binding to Coomassie blue), lipid (gravimetrically) and mineral (spectrophotometrically) contents. The milk lactose concentration of group H increased with stage of lactation (r2 0.85, P < 0.001). Such an increase was prevented by diet L, and from day 8 of lactation the milk lactose of group L was lower (P < 0.05) than in group H. Group H milk protein concentration did not change during lactation and averaged 90.7 mg/g. Dietary protein restriction reduced the milk protein concentration of group L so that on days 2, 4 and 12 of lactation it was lower (P < 0.05) than that of group H. On day 8 of lactation the milk protein concentration of group L had increased (P < 0.05) and was comparable with that of group H. For group H, milk lipid averaged 166.8 mg/g and was generally unchanged during lactation. Diet L increased (P < 0.01) the milk lipid concentration (205.5 mg/g) compared with diet H and this was also significant on days 4 and 8 of lactation (P < 0.05). Group L milk lipid concentration also increased between days 4 and 8 of lactation (P < 0.05). Milk Na concentration declined during lactation in both dietary groups (P < 0.01) but was unaffected by dietary treatment. Both milk Ca and P concentrations increased (P < 0.01) during lactation in both dietary groups, whilst protein restriction also increased the Ca and P concentrations (P < 0.05). Milk K and Mg concentrations were unaffected by dietary treatment or stage of lactation. This significant alteration in the milk composition of severely protein-restricted dams, while possibly favouring the disposal of greater quantities of energy-yielding nutrients, suggests that equations developed for the estimation of milk production in rats cannot be used under such conditions.

Maternal protein reserves and their influence on lactational performance in rats. 2. Effects of dietary protein restriction during gestation and lactation on tissue protein metabolism and Na+, K(+)-ATPase (EC 3.6.1.3) activity.

Changes in tissue protein synthesis and an associated membrane transport system in rats were investigated during lactation and under conditions of dietary protein restriction. Following mating, female Sprague-Dawley rats (second parity) were caged individually and offered a high-protein diet (H; 215 g crude protein (N x 6.25; CP)/kg dry matter (DM)) ad lib. until day 12 of gestation. Subsequently half continued to receive diet H, whilst the remainder were offered a low-protein diet (L; 65 g CP/kg DM) until parturition. On day 1 of lactation females were then allocated to either diet H or another low-protein diet (L2; 90 g CP/kg DM) which were offered ad lib. until day 13 of lactation, giving four lactation groups HH, LH, HL2 and LL2. On days 1 and 13 of lactation groups of females were used in the estimation of tissue protein synthesis (flooding dose of [3H] phenylalanine) and Na+, K(+)-ATPase (EC 3.6.1.3) activity (polarographically) in skeletal muscle, mammary gland, liver and duodenal mucosa. By day 1 of lactation diet L had reduced fractional and absolute synthesis rates (FSR and ASR) of muscle protein (P < 0.05) and the O2 consumption associated with Na+, K(+)-ATPase, although not significantly (P < 0.10). Rates of protein synthesis in the other tissues studied were not affected on day 1 of lactation by the gestation dietary treatment. By day 13 of lactation the feeding of diet L2 had reduced muscle FSR and ASR of group HL2 to rates that were lower than those on day 1 (P < 0.05), comparable to those of group LL2 and lower than those of groups HH and LH (P < 0.05). Diet H had allowed group LH to increase their muscle protein synthesis compared with that on day 1 (P < 0.05). Muscle Na+, K(+)-ATPase activity on day 13 of lactation was also lower in groups offered diet L2 (P < 0.05). Mammary protein synthesis was increased during lactation with the feeding of diet H (P < 0.05), which was prevented by diet L2 such that rates of groups HL2 and LL2 were lower than those of the two high-protein groups on day 13 (P < 0.01). Mammary respiration and in particular Na+, K(+)-ATPase activity was increased during lactation by the feeding of diet H (P < 0.05). Rates of protein synthesis and respiration in liver and duodenal mucosa were not significantly affected by the gestational or lactational dietary treatments.(ABSTRACT TRUNCATED AT 400 WORDS)

Maternal protein reserves and their influence on lactational performance in rats.

To determine the contribution of tissue protein reserves to lactational performance, multiparous female Sprague-Dawley rats were mated, caged individually and offered a diet high in protein (215 g crude protein (N x 6.25; CP)/kg dry matter (DM); H) ad lib. until day 12 of gestation. Subsequently half the rats continued to receive diet H while the remainder were offered a diet low in protein (65 g CP/kg DM; L) until parturition. This treatment aimed to produce a difference in carcass protein at parturition. On day 1 of lactation females were allocated to either diet H or a low-protein diet (90 g CP/kg DM; L2) offered until day 13 of lactation, giving four lactation treatment groups HH, HL2, LH and LL2. Groups of females were slaughtered on days 2 and 12 of gestation and days 1 and 13 of lactation and carcass and major organs were analysed. Weight gain of standardized litters was used as an indicator of lactational performance. Maternal carcass protein contents at parturition were 43.5 (SE 1.2) and 38.7 (SE 0.8) g (P < 0.01) for diets H and L respectively. During lactation there was little change in carcass protein content of HH rats while LH rats appeared to replenish their depleted reserves. Food intake or lactational performance did not differ between these two groups. HL2 and LL2 rats lost carcass protein with HL2 rats losing more than LL2 rats (P < 0.05). Intake and lactational performance were reduced compared with that on diet H (P < 0.05) but for the first 6 d of lactation were both greater (P < 0.05) for diet HL2 than for diet LL2. All four groups showed a considerable loss of body fat during lactation which was not affected by diet. The ability of HL2 rats to catabolize more protein and consume more food allowed them to sustain a greater lactational performance. Previous maternal protein depletion had no influence on lactational performance as long as an adequate supply of dietary protein was provided.