The objective of this study was to evaluate local molecular adaptations proposed to regulate protein synthesis in the mammary glands. It was hypothesized that AA and energy-yielding substrates independently regulate AA metabolism and protein synthesis in mammary glands by a combination of systemic and local mechanisms. Six primiparous mid-lactation Holstein cows with ruminal cannulas were randomly assigned to 4 treatment sequences in a replicated incomplete 4 x 4 Latin square design experiment. Treatments were abomasal infusions of casein and starch in a 2 x 2 factorial arrangement. All animals received the same basal diet (17.6% crude protein and 6.61 MJ of net energy for lactation/kg of DM) throughout the study. Cows were restricted to 70% of ad libitum intake and abomasally infused for 36 h with water, casein (0.86 kg/d), starch (2 kg/d), or a combination (2 kg/d starch+0.86 kg/d casein) using peristaltic pumps. Milk yields and composition were assessed throughout the study. Arterial and venous plasma samples were collected every 20 min during the last 8h of infusion to assess mammary uptake. Mammary biopsy samples were collected at the end of each infusion and assessed for the phosphorylation state of selected intracellular signaling molecules that regulate protein synthesis. Animals infused with casein had increased arterial concentrations of AA, increased mammary extraction of AA from plasma, either no change or a trend for reduced mammary AA clearance rates, and no change in milk protein yield. Animals infused with starch had increased milk and milk protein yields, increased mammary plasma flow, reduced arterial concentrations of AA, and increased mammary clearance rates and net uptake of some AA. Infusions of starch increased plasma concentrations of glucose, insulin, and insulin-like growth factor-I. Starch infusions increased phosphorylation of ribosomal protein S6 and endothelial nitric oxide synthase, consistent with changes in milk protein yields and plasma flow, respectively. Phosphorylation of the mammalian target of rapamycin was increased in response to starch only when casein was also infused. Thus, cell signaling molecules involved in the regulation of protein synthesis differentially responded to these nutritional stimuli. The hypothesized independent effects of casein and starch on animal metabolism and cell signaling were not observed, presumably because of the lack of a milk protein response to infused casein.

The aim of this study was to test whether feeding of diets containing lower proportions of ruminally degradable protein (RDP) but with a constant proportion of ruminally undegradable protein (RUP) alters feed intake, milk production and yield, and the apparent efficiency of N utilization by mid-lactation dairy cows. During the covariate period (d 1 to 28), 40 mid-lactation cows (36 Holstein and 4 Jersey x Holstein cross-breds) were fed a common diet formulated to contain 11.3% of diet dry matter (DM) as RDP. During the treatment period (d 29 to 47), cows were randomly assigned to 1 of 4 diets formulated to contain 11.3, 10.1, 8.8, or 7.6% RDP, whereas ruminally undegradable protein remained constant at 7.1% of DM. All diets contained 47.5% forage and 52.5% concentrate on a DM basis. Dry matter intake was significantly reduced for the 7.6% RDP diet. The lowest RDP content was associated with a trend for reduced milk yield. Dietary RDP had no effect on body weight or milk fat, protein, and lactose contents. Milk protein yield was not affected by RDP level; however, milk fat yield decreased linearly as dietary RDP was reduced. Concentrations of plasma essential amino acids were unaffected, whereas milk urea-N concentrations decreased linearly as dietary RDP content was reduced. The apparent efficiency of N utilization for milk N production increased from 27.7% on the 11.3% RDP diet to 38.6% on the 7.6% RDP diet. The dietary RDP requirement of cows in this study was apparently met between 15.9 and 14.7% dietary crude protein. Milk production was not significantly affected by the 8.8% RDP (15.9% crude protein) diet even though the NRC (2001) model predicted that RDP supply was 87% of that required, suggesting the current NRC recommendations for RDP may be overestimated for mid-lactation dairy cows in this study.

This study was conducted to determine the potential for reducing ammonia (NH3) emissions from manure deposited on the floor of a naturally ventilated free stall barn by mid-lactation dairy cows fed reduced or normal N diets. Two crude protein (CP) diets (178 g kg(-1) [high] and 159 g kg(-1) [low] dry matter ), were used. The diets were fed to 48 Holstein cows in a replicated crossover design with two pens per diet. The NH3 emitted from the manure deposited on the floor was measured using a dynamic flux chamber. The NH3 emissions were 2.7 (+/-2.0) and 2.9 (+/-1.8) g N cow(-1) d(-1) for high and low CP diets, respectively. Ammonia emission rates were significantly affected by manure pH, TKN, and ambient air temperature (P<0.05). Dietary CP affected the feed N intake (8.7 and 7.1 kg pen(-1) d(-1) for high and low CP, respectively), but did not affect milk yield (500 and 489 kg pen(-1) d(-1) for high and low CP, respectively) and milk CP content (30 g kg(-1) for both the high and low CP diets). The N utilization efficiency was 29.0% and 32.7% for the high and low CP diets, respectively. Reducing dietary CP reduced total Kjeldahl N (TKN) in manure, but did not affect the total ammoniacal N (TAN) in manure and had no significant effect on the ammonia emission rates from the barn floor.

The nutrient content of and feeding recommendations for milk replacers (MR) vary widely in North America, and acceleration of growth through manipulation of protein and energy intakes can reduce rearing costs of dairy operations. The effects of varying the protein and energy intake of MR on metabolite concentrations in plasma, liver, and muscle and the phosphorylation activity of protein kinase B (AKT) and ribosomal protein S6 (rpS6) cell signals in liver and muscle were assessed. Twenty-four newborn Holstein calves were fed 1 of 4 MR for 9 wk (n=6/treatment): (1) a 20% crude protein (CP), 20% fat MR fed at 441 g of dry matter (DM)/d (CON); (2) a high-protein, medium-fat MR (HPMF; 28% CP, 20% fat) fed at 951 g of DM/d; (3) a high-protein, high-fat MR (HPHF; 27% CP, 28% fat) fed at 951 g of DM/d; and (4) HPHF fed at 1,431 g of DM/d (HPHF+). Water and starter (20% CP, 1.43% fat) were offered ad libitum and calves were fed MR twice daily. Plasma samples were obtained at 1, 5, and 9 wk of age. Calves were not weaned and were slaughtered after the last blood sampling. Liver and muscle tissues were collected and analyzed for metabolite concentrations and cell signaling activity. Calves fed all treatments had lower plasma concentrations of Phe and Tyr, and a trend for lower Leu, but greater concentrations of Thr relative to calves fed CON. Calves fed all treatments had increased muscle concentrations of Met and muscle to plasma ratios of Phe, Tyr, and branched-chain amino acids compared with CON. All treatments increased liver to plasma ratios of Phe and Tyr but diminished the ratios of Met compared with CON. Phosphorylation of protein kinase B was not affected by treatment; however, relative to calves fed HPHF, HPMF and HPHF+ diets increased phosphorylation ratios of ribosomal protein S6 in the liver. Therefore, the changes in plasma and tissue concentrations and plasma to tissue ratios of amino acids were associated with enhanced growth rates. However, cell signaling activity was not consistent with accelerated growth in calves fed treatments with increased contents of energy and protein possibly due to confounding effects of diet (MR + starter) or fasting before tissue harvesting. Muscle concentrations of Met might have a regulatory role in protein synthesis in rapidly growing calves fed high levels of CP and energy.

An improved understanding of the potential for dietary protein manipulation to reduce ammonia emissions from dairy farms during various stages of manure handling is needed for both modeling and policy-making efforts. The objective of this study was to assess the effects of dietary protein manipulation on ammonia emissions from relatively freshly voided dairy cow manure in three types of removal systems: scraped manure removal systems, flushed manure removal systems, and flushed manure removal systems with a solids separator. Emissions were measured using a dynamic flux chamber for 12 h or more. Ammonia fluxes and emission factors per mass of manure were not affected by dietary protein content because fluxes depended mainly on total ammoniacal nitrogen (TAN) concentration, which did not vary with diet. However, emissions on a per-cow basis were 12% lower with the diet containing 15.0% crude protein as compared to the one with 17.8% (a change in crude protein of 16%) due to reduced urine output. The largest absolute impact of dietary protein manipulation would be with separated liquids because their emission factor was approximately four times higher than for the other types of manure. While dietary protein manipulation can reduce ammonia emissions from manure during long-term storage, its effectiveness in the hours immediately after manure is excreted is limited because emissions are more sensitive to other factors, including temperature and extent of mixing of the manure, that vary widely under real operating conditions on a farm.