Saccharomyces cerevisiae is a key component of beer brewing and a major by-product. The leftover, spent brewers' yeast from large breweries has been used as a protein supplement in cattle; however the possible advantages of spent yeast from smaller craft breweries, containing much higher levels of bioactive hop acids, have not been evaluated. Hops secondary metabolites from the hops (Humulus lupulus L.) used to make beer are concentrated in the yeast during brewing, and have antimicrobial activity against Gram-positive bacteria. Uncultivated suspensions of bovine rumen microorganisms produced less methane during fructose fermentation when exposed to inactivated, and freeze-dried spent craft brewers' yeast than a bakers' yeast control. The experiment was repeated with caprine rumen microorganisms and ground grass hay as the substrate. Likewise, in the presence of craft brewers' yeast less methane was produced (2.7% vs. 6.9% CH4). Both experiments also revealed a decrease in acetic acid production, but not propionic acid production, when craft brewers' yeast was included. These results indicated that spent yeast could represent a co-product for craft breweries, and a feed supplement for ruminants that has a favorable impact on methane production.

Background Understanding the mechanisms of N utilization for lactation can lead to improved requirement estimates and increased efficiency, which modern dairy diets currently fail to maximize. The mechanistic target of rapamycin complex 1 (mTORC1) is a central hub of translation regulation, processing extra- and intra-cellular signals of nutrient availability and physiological state, such as amino acids and energy. We hypothesized that dietary amino acids regulate lactation through mTORC1, such that inhibition of mTORC1 will lead to decreased lactation performance when amino acids are not limiting. Our objectives were to assess lactation performance in lactating mice undergoing dietary and pharmacologic interventions designed to alter mTORC1 activity. Methods First lactation mice (N = 18; n = 6/treatment) were fed an adequate protein diet (18% crude protein), or an isocaloric protein-restricted diet (9% crude protein) from the day after parturition until lactation day 13. A third group of mice was fed an adequate protein diet and treated with the mTORC1 inhibitor rapamycin (4 mg/kg every other day) intraperitoneally, with the first two groups treated with vehicle as control. Dams and pups were weighed daily, and feed intake was recorded every other day. Milk production was measured every other day beginning on lactation day 4 by the weigh-suckle-weigh method. Tissues were collected after fasting and refeeding. Results Milk production and pup weight were similarly decreased by both protein restriction and rapamycin treatment, with final production at 50% of control (P = 0.008) and final pup weight at 85% of control (P < 0.001). Mammary phosphorylation of mTORC1’s downstream targets were decreased by protein restriction and rapamycin treatment (P < 0.05), while very little effect was observed in the liver of rapamycin treated mice, and none by protein restriction. Conclusions Overall, sufficient supply of dietary amino acids was unable to maintain lactation performance status in mice with pharmacologically reduced mammary mTORC1 activity, as evidenced by diminished pup growth and milk production, supporting the concept that mTORC1 activation rather than substrate supply is the primary route by which amino acids regulate synthesis of milk components.

Increased milking frequency and incomplete milking have differential effects on milk yield and mammary gland physiology that are important for optimization of milking practices in dairy herds. The objectives of this experiment were to determine the effects of increased milking frequency and incomplete milking on milk production rate (MPR) and milk composition and to determine if milking 3 times daily (3×) could rescue the negative production effects of incomplete milking. Twenty-two multiparous cows were enrolled onto this experiment beginning at 5 days in milk (DIM) and continuing through 47 DIM. A split-plot design was used to randomize the 2 treatments, which were milking frequency and incomplete milking. Eleven cows were randomly assigned to be milked 2 times (2×) daily and 11 cows were randomly assigned to be milked 3×. Within each cow, a contralateral half-udder was randomly assigned to be incompletely milked (30% milk remaining in the gland; IM), and the other half-udder was randomly assigned to be milked completely (CM). Quarter-level milk yields were recorded at each milking session. Milk samples from all quarters were collected twice weekly at the beginning of the morning milking for analysis. Cows milked 2× tended to have reduced MPR compared with 3× milked cows (1.81 ± 0.06 vs. 1.97 ± 0.06 kg milk/h; P = 0.06). Half-udders that were CM and IM produced 1.09 ± 0.03 and 0.80 ± 0.03 kg milk/h, respectively. There was an interaction between incomplete milking treatment and week of lactation (P = 0.04). No interaction was detected between milking frequency and incomplete milking for MPR or milk components. Cows milked 3× had increased milk fat percent (1.93 ± 0.09% vs. 1.65 ± 0.09%, P = 0.047), decreased milk lactose percent (4.80 ± 0.04% vs. 4.93 ± 0.04%, P = 0.04), and exhibited no differences in milk protein percent or milk somatic cell count (SCC) compared with cows milked 2×. Half-udders that were IM had increased milk fat percent (2.15 ± 0.07% vs. 1.43 ± 0.07%, P &lt; 0.0001), decreased lactose percent (4.75 ± 0.03% vs. 4.99 ± 0.03%, P &lt; 0.0001), increased milk log10SCC (4.22 ± 0.05 vs. 4.41 ± 0.05, P = 0.0004), and no differences in milk protein percent compared with CM half-udders. These results indicate that a 3× milking frequency in IM half-udders was not able to improve milk production compared with IM half-udders milked 2×. Our results indicate that 30% milk remaining in the gland had an irreversible impact on milk yield as increased milking frequency was not able to reverse the milk yield lost.

For dairy production systems, nitrogen is an expensive nutrient and potentially harmful waste product. With three quarters of fed nitrogen ending up in the manure, significant research efforts have focused on understanding and mitigating lactating dairy cows’ nitrogen losses. Recent changes proposed to the Nutrient Requirement System for Dairy Cattle in the US include variable efficiencies of absorbed essential AA for milk protein production. This first separation from a purely substrate-based system, standing on the old limiting AA theory, recognizes the ability of the cow to alter the metabolism of AA. In this review we summarize a compelling amount of evidence suggesting that AA requirements for milk protein synthesis are based on a demand-driven system. Milk protein synthesis is governed at mammary level by a set of transduction pathways, including the mechanistic target of rapamycin complex 1 (mTORC1), the integrated stress response (ISR), and the unfolded protein response (UPR). In tight coordination, these pathways not only control the rate of milk protein synthesis, setting the demand for AA, but also manipulate cellular AA transport and even blood flow to the mammary glands, securing the supply of those needed nutrients. These transduction pathways, specifically mTORC1, sense specific AA, as well as other physiological signals, including insulin, the canonical indicator of energy status. Insulin plays a key role on mTORC1 signaling, controlling its activation, once AA have determined mTORC1 localization to the lysosomal membrane. Based on this molecular model, AA and insulin signals need to be tightly coordinated to maximize milk protein synthesis rate. The evidence in lactating dairy cows supports this model, in which insulin and glucogenic energy potentiate the effect of AA on milk protein synthesis. Incorporating the effect of specific signaling AA and the differential role of energy sources on utilization of absorbed AA for milk protein synthesis seems like the evident following step in nutrient requirement systems to further improve N efficiency in lactating dairy cow rations.

Corrigendum to: "The effects of incomplete milking and increased milking frequency on milk production rate and milk composition" by Jordan M. Kuehnl et al.