Effects of Amount and Profile of Amino Acids Supply on Lactation Performance, Mammary Gland Metabolism, and Nitrogen Efficiency in Holstein Dairy Cows.

To evaluate the effects of amount and profile of amino acid (AA) on milk protein yield (MPY), mammary metabolism, and efficiency of nitrogen use (ENU), ten cows were used in 5 × 5 replicated Latin squares and fed a positive control (16.1% crude protein-CP) or two lower CP diets (14.6 and 13.2%) with or without essential AA (EAA) infusion. The EAA solutions provided predicted limiting EAA in each treatment and were continuously infused into the abomasum of the cows. Milk production and MPY were not affected by treatment (mean 35.4 kg/d and 1.03 kg/d, respectively). Efficiency of nitrogen utilization was increased as dietary CP decreased but was not affected by EAA infusion (p < 0.01). Energy-corrected milk production was increased by EAA infusion into 13.2% CP, but not into 14.6% CP diet (p = 0.09), reaching the positive control value. Infusions increased mammary affinity for non-infused EAA (Ile, Phe, Thr, and Trp), allowing the same MPY despite lower arterial concentrations of these AA. Higher arterial concentrations of infused EAA did not increase their mammary uptake and MPY (p = 0.40; p = 0.85). Mammary metabolism did not fully explain changes in N efficiency, suggesting that it might be driven by less extramammary catabolism as AA supply was reduced.

Brief, Written Reflections Improve Interest of Introductory Animal Science Undergraduates.

In addition to stimulating interest through experiential means, educators can support interest development through structured reflection. Our randomized controlled intervention study assessed the effectiveness of 10-minute written utility-value reflections designed to enhance the interest of introductory animal science students. During the Spring 2019 semester, we randomly assigned participating students into two blocks, utility-value reflection (n = 39) and control (n = 34), at the beginning of the course. In week 6 during the 16-week semester, students completed corresponding tasks: either written reflections on the personal value of course laboratory material or a control picture-summarization task. Results showed that the utility-value reflection intervention tended to improve situational interest and was most effective for students with low pretest individual interest. Neither the intervention nor the interest variable predicted course performance. In utility-value reflection responses, we catalogued themes aligned with a range of task-value components beyond utility-value. Our results reinforce previous work indicating that utility-value reflections support low individual interest students in developing academic motivation.

Effect of rumen-protected lysine supplementation of diets based on corn protein fed to lactating dairy cows.

This trial tested whether rumen-protected Lys (RPL) supplementation would improve the nutritive value of rumen-undegradable protein (RUP) from corn protein. Thirty-two lactating Holstein cows were blocked by days in milk and parity into 8 squares of 4 cows each in replicated 4 × 4 Latin squares. Treatments provided all supplemental crude protein from: (1) soy protein (67% expeller soybean meal plus 33% solvent soybean meal); (2) a blend of soy and corn protein (33% expeller soybean meal, 17% solvent soybean meal, 25% corn gluten meal plus 25% distillers dried grains with solubles); (3) corn protein (50% corn gluten meal plus 50% distillers dried grains with solubles); or (4) corn protein plus RPL [diet 3 top-dressed with RPL (125 g/d of AjiPro-L Generation 1, supplying an estimated 20 g of absorbable Lys/d)]. Diets contained (dry matter basis) 22% alfalfa silage, 43% corn silage, 18% ground high-moisture and dry corn, 2.4% mineral-vitamin premix, 1.5 to 3.9% soy hulls, 15% crude protein, 30 to 32% neutral detergent fiber and predicted to contain equal rumen-degradable protein, RUP, and metabolizable protein. Cows within squares were randomly assigned to treatment sequences and fed diets for 4-wk periods before switching; production data and blood samples were collected during last 2 wk of each period. Data were analyzed using the mixed procedures of SAS. Intake was highest on diet 1, intermediate on diets 2 and 3, and lowest on diet 4; body weight gain was highest on diet 3, intermediate on diets 1 and 2 and lowest on diet 4. Intakes and body weight changes were reflected by differences in milk/dry matter intake, which was highest on diets 2 and 4 and lowest on diet 3. Milk yield was lower on diet 3 (44.3 kg/d) than on diets 1, 2, and 4 (average 45.8 kg/d) and protein yield was highest on diets 1 and 2 (average 1.35 kg/d), intermediate on diet 4 (1.30 kg/d), and lowest on diet 3 (1.25 kg/d). No effects of diet were detected on ruminal metabolites. Free nonessential amino acids and total protein AA were elevated in blood plasma on diet 3, reflecting reduced utilization for milk protein synthesis. These results indicated that 50% dilution of soybean meal RUP with that from corn protein did not reduce yield and that supplementing RPL to the corn protein-based diet increased yield 1.1 kg of milk/d and 50 g of true protein/d.

Local feeding strategies and milk composition in small-scale dairy production systems during the rainy season in the highlands of Mexico.

The objective of the work was to identify local feeding strategies in small-scale dairy production systems during the rainy season in the highlands of Mexico, and to determine their effects on milk yields (MY), milk composition and economic viability. Twenty-two dairy farms were monitored by monthly visits, recording and sampling milk from between two and six cows in each farm, live-weight was also recorded. Samples from feeds used in that month were taken and feeds given to the dairy herd were weighed. Economic data was also recorded. Milk composition and milk urea nitrogen were determined, as well as chemical composition of feeds. Eighteen feedstuffs were identified, grouped in: HNH feeds-high in neutral detergent fibre (NDF) and in DM matter; HNL feeds-high in NDF but low in DM; HCh feeds-high in non-fibrous carbohydrates; and HCP feeds-high in crude protein. Four feeding strategies were identified: strategy 1 uses HND, HNL and HCP; strategy 2-HND, HNL, HCh and HCP; strategy 3 HNH and HCP; and strategy 4 HNL and HCP. Of participating farms, 73.4% followed strategy 1, 11.3% strategy 2, 11.3% strategy 4 and 3.8% strategy 3. There were no statistical differences (P > 0.05) between strategies for MY and milk composition, but there were differences (P < 0.05) for ration costs. Multiple regression analysis showed no significative (P > 0.05) model relating intake of feed groups and milk fat content, but milk protein and SNF contents were significantly explained by intake of HCP. When expressed as MY and milk components yield, milk fat yield was significantly explained by intake of all four feed groups, but milk protein and SNF yields were explained only by intake of HCP and LW. MUN excretion was explained also by HCP intake. All feeding strategies produced positive economic returns, on average generating the equivalent of 3.45 minimum wages of the area.