Reducing dietary crude protein: Effects on digestibility, nitrogen balance, and blood metabolites in late-lactation Holstein cows.

Our objectives were to determine the effects of reducing dietary CP concentration on nutrient digestibility, rumen function, N balance, and serum AA concentration for dairy cows in late lactation. At the initiation of the experimental period, we stratified Holstein cows (n = 128; mean ± SD 224 ± 54 DIM) by parity and days pregnant (86 ± 25 d) and assigned them to 1 of 16 pens. For 3 wk, all cows received a covariate diet containing 16.9% CP (DM basis). For the subsequent 12 wk, we assigned pens to 1 of 4 treatments containing 16.2%, 14.4%, 13.4%, or 11.9% CP (DM basis) in a randomized complete block design. Diets were fed as a TMR once daily. To reduce dietary CP, we replaced soybean meal with soybean hulls in the concentrate mix (DM basis). Diet evaluations suggested that several EAA, especially His, limited productivity as dietary CP declined. Digestibility of DM and CP decreased linearly with dietary CP reduction. Digestibility of NDF and potentially digestible NDF tended to respond in a quadratic pattern with the greatest digestibility at intermediate treatments. The reduction in dietary CP did not affect ruminal pH, but ruminal ammonia-N and branched-chain VFA concentrations declined linearly. The concentration of milk urea-N and plasma urea-N, secretion of milk N, and excretions of fecal N, urinary N, urinary urea-N, and unaccounted N decreased linearly with the reduction in dietary CP concentration. Urinary N expressed as a percentage of N intake was unaffected by dietary CP. Serum concentrations of total essential AA and NEAA were unaffected by dietary CP concentration. However, the ratio of essential to NEAA decreased with decreasing dietary CP. Serum 3-methylhistidine concentration increased linearly with decreasing dietary CP concentration, indicating greater skeletal muscle breakdown. Although our trial confirmed that reducing dietary CP decreased absolute excretion of urinary N, diet evaluations suggested that milk protein production decreased as certain essential AA became increasingly limited. Thus, reduced-CP diets have the potential to lessen reactive-N outputs of late-lactation cows, but more research is needed to design diets that minimize deleterious effects on productivity.

Crude protein oscillation in diets adequate and deficient in metabolizable protein: Effects on nutrient digestibility, nitrogen balance, plasma amino acids, and greenhouse gas emissions.

Reducing dietary CP is a well-established means to improve N use efficiency. Yet, few studies have considered if transient restrictions in dietary CP could reduce the environmental footprint of late-lactation cows. We hypothesized that the effects of CP feeding pattern on digestibility and environmental outputs would be amplified at lower dietary CP. We tested CP levels below and near predicted requirements (low protein [LP], 13.8%; high protein [HP], 15.5%) offered in 2 feeding patterns: where diets alternated ±1.8 percentage units CP every 2 d (oscillating [OF]) or remained static. Our study used a 2 × 2 factorial design with 16 mid- to late-lactation Holsteins (mean = 128, SD = 12 DIM), divided into rumen-cannulated (n = 8) and noncannulated subsets (n = 8). For each 28-d experimental period, we recorded feed intake and milk production and took samples of orts (1×/d) and milk (2×/d) for 4 d. For the cannulated subset, we measured and sampled from the total mass of feces and urine production and collected plasma 2×/d across 4 d. For the noncannulated subset, we sampled carbon dioxide and methane emissions 3×/d for 4 d. For each subset, we fit linear mixed models with fixed effects for CP level, CP feeding pattern, the interaction of CP level and CP feeding pattern, period, and a random effect for cow. For plasma and urinary urea-N, we conducted time series analysis. Contrary to our hypothesis, we found no evidence that dietary CP level and CP feeding pattern interacted to influence N balance, nutrient digestibility, or gas emissions. Results showed HP resulted in similar milk N but increased manure N, reducing N use efficiency (milk true protein N/intake N) relative to LP. For OF, urea-N in urine and plasma peaked 46 to 52 h after the first higher-CP phase feeding. Nutrient digestibility and gas emissions were similar across treatments, except CO2 production was greater for OF-HP. In summary, measured variables were minimally affected by dietary CP alternating ±1.8 percentage units every 48 h, even when average dietary CP was fed below predicted requirements (LP). Although our findings suggest that mid- to late-lactation cows are resilient to oscillation in dietary CP, oscillating CP neither reduced the environmental footprint by improving nutrient use efficiencies nor reduced the potential for direct and indirect greenhouse gas emissions.

Dynamic lactation responses to dietary crude protein oscillation in diets adequate and deficient in metabolizable protein in Holstein cows.

Limited research has examined the interaction between dietary crude protein (CP) level and CP feeding pattern. We tested CP level (low protein [LP], 13.8%; high protein [HP], 15.5% CP, dry matter [DM] basis) and CP feeding pattern (OF = oscillating, SF = static) using a 2 × 2 factorial in 16 mid- to late-lactation Holsteins (initially 128 ± 12 d in milk; mean ± SD). Cows ate total mixed rations formulated by exchanging soy hulls and ground corn with solvent soybean meal to keep constant ratios of neutral detergent fiber to starch (1.18:1), rumen-degradable protein to CP (0.61:1), and forage-to-concentrate (1.5:1) in DM. The OF treatments alternated diets every 48 h to vary CP above and below the mean CP level (OF-LP = 13.8% ± 1.8%; OF-HP = 15.5% ± 1.8% CP [DM basis]) whereas diets were constant in SF (SF-LP = 13.8%; SF-HP = 15.5% CP [DM basis]). In four 28-d periods, 8 rumen-cannulated and 8 noncannulated cows formed 2 Latin rectangles. On d 25 to 28 of each period, each cow's feed intake and milk production were recorded, and samples were taken of orts (1×/d) and milk (2×/d). We fit linear mixed models with fixed CP level, CP feeding pattern, and period effects, and a random intercept for cow, computing least squares means and standard errors. Neither CP level, CP feeding pattern, nor the interaction affected DM intake, feed efficiency, or production of milk, fat- and protein-corrected milk (FPCM), fat, true protein, or lactose. Milk urea-N (MUN) yield was lesser for LP. The LP and OF conditions decreased MUN concentration. The CP level tended to interact with CP feeding pattern so that milk protein concentration was greatest for OF-HP. The OF and LP conditions increased the ratio of true protein to MUN yield. Within OF, cosinor mixed models of selected variables showed that cows maintained production of FPCM across dietary changes, but MUN followed a wave-pattern at a 2-d delay relative to dietary changes. A tendency for lesser MUN with OF contradicted prior research and suggested potential differences in urea-N metabolism between OF and SF. Results showed that cows maintained production of economically-relevant components regardless of CP feeding pattern and CP level. Contrary to our hypothesis, the effects of 48-h oscillating CP were mostly consistent across CP levels, suggesting that productivity is resilient to patterned variation in dietary CP over time even when average CP supply is low (13.8% of DM) and despite 48 h restrictions at 12.2% CP.

Short communication: Decreasing the dietary ratio of n-6 to n-3 fatty acids increases the n-3 concentration of peripheral blood mononuclear cells in weaned Holstein heifer calves.

Utilization of nutrients to improve overall heifer health is of interest because of the importance of replacement heifers to the dairy industry. The objective of our study was to compare the effect of supplementation of dietary n-3 and n-6 fatty acids (FA) on FA concentrations in peripheral blood mononuclear cells (PBMC) of Holstein calves. Twenty-seven Holstein heifer calves (107 ± 2.6 d of age; 142.6 ± 6.5 kg of body weight) from the university research and teaching herd were randomly assigned to a common TMR supplemented with 1 of 3 treatments: Ca salts of flaxseed FA (Virtus Nutrition, Corcoran, CA) containing 35% 18:3 n-3 (N3), Ca salts of soybean FA (Virtus Nutrition) containing 50% 18:2 n-6 (N6), or a 50:50 mix of N3 and N6. Treatments were supplemented with FA at 4% of dietary dry matter and fed for 30 d. Feed intake was recorded daily, and body weight, wither height, and body condition score were measured weekly throughout the study. On d 28 heifers were vaccinated with a Pasteurella vaccine and the temperature response to the vaccine was recorded. Blood was collected on d 0 and 28 for PBMC isolation. After total lipid extraction and FA methyl ester preparation, FA composition of PBMC was measured. We observed no effect of treatment on body weight gain, body condition score change, or wither height change. Heifers receiving the N3 diet had a lower temperature response to Pasteurella challenge compared with both the mix and N6 diets. Heifers consuming the N3 diet had a greater content of total n-3 FA, α-linolenic acid, and eicosapentaenoic acid in PBMC compared with heifers fed the N6 and mix diets. Heifers receiving the N3 diet also had a lower content of total n-6 FA, linoleic acid, and arachidonic acid in PBMC than heifers fed the N6 and mix diets. In conclusion, our study determined that feeding weaned female Holstein heifers a diet high in n-3 FA increased concentrations of n-3 FA in PBMC.

Animal sciences undergraduate education since the ASAS centennial: a national survey and scoping review.

The rapid pace of advancement in animal sciences is drastically changing conditions for undergraduate teaching and learning in the discipline. Shortly after the American Society of Animal Science (ASAS) centennial, we conducted a national survey of 90 faculty instructors from 49 academic institutions to assess their perceptions of emerging teaching topics. Participants rated 18 learning outcomes (LO) and 16 types of courses and experiences (CE) with respect to their importance and the adequacy of available offerings. This study presents the results of the survey along with a scoping review of animal sciences teaching and learning publications since 2008 (n = 71). Results indicated that discipline-specific competencies and core experiential learning remain central to animal sciences teaching and identified several distinct needs for research. Namely, we suggest that future research in animal sciences teaching and learning 1) develop animal-science-specific expertise on a greater variety of pedagogies, 2) validate improved methods for assessing transferable skills, 3) expand pedagogical knowledge of emerging topics (e.g., sustainability, data science, welfare science, social science), and 4) deepen and broaden animal sciences' teaching and learning identity through theory-building work and collaborations across instructors, disciplines, and institutions.

Preassociation of calmodulin with voltage-gated Ca(2+) channels revealed by FRET in single living cells.

Among the most intriguing forms of Ca(2+) channel modulation is the regulation of L-type and P/Q-type channels by intracellular Ca(2+), acting via unconventional channel-calmodulin (CaM) interactions. In particular, overexpressing Ca(2+)-insensitive mutant CaM abolishes Ca(2+)-dependent modulation, hinting that Ca(2+)-free CaM may "preassociate" with these channels to enhance detection of local Ca(2+). Despite the far-reaching consequences of this proposal, in vitro experiments testing for preassociation provide conflicting results. Here, we develop a three filter-cube fluorescence resonance energy transfer method (three-cube FRET) to directly probe for constitutive associations between channel subunits and CaM in single living cells. This FRET assay detects Ca(2+)-independent associations between CaM and the pore-forming alpha(1) subunit of L-type, P/Q-type, and, surprisingly, R-type channels. These results now definitively demonstrate channel-CaM preassociation in resting cells and underscore the potential of three-cube FRET for probing protein-protein interactions.