Production responses of high producing Holstein cows to ruminally protected phenylalanine and tyrosine supplemented to diets containing high levels of canola meal

Abstract

Phenylalanine (Phe) was first identified as a potentially limiting amino acid (AA) in lactating dairy cows in 1974. There is the possibility that conversion of Phe to tyrosine (Tyr) is not efficient enough to supply all Tyr requirements for milk production in high producing dairy cows, thereby suggesting that Tyr itself could become a functionally limiting AA when it, and/or Phe, is not supplied to the mammary gland in adequate quantities. Our objective was to determine if previous positive responses of lactating cows to Phe supplementation when fed a diet containing high levels of canola meal (CM) could be improved by supplying Tyr in place of some Phe. The experimental design was a 4×4 Latin square using 4 pens of ∼315 early lactation multiparous cows/pen with four 21 d periods. Diets were formulated to include a low CM treatment (LCM) containing CM at ~120 g CM/kg dry matter (DM) and a high CM treatment (HCM) with CM at ~170 g CM/kg DM. The other two treatments were the HCM diet, but with Phe (HCM+P) or Phe plus Tyr (HCM+PT) added in a ruminally protected (RP) form. The DM intake tended (P=0.10) to decline, but milk yield did not differ, between the LCM and HCM treatments, while milk fat, lactose and energy output was lower (P<0.02) with the HCM treatment, and body condition score (BCS) gain was enhanced (P<0.01). Adding Phe to the HCM diet had little impact on milk and component yields, but a positive BCS gain of 0.056 units/28 d decreased (P<0.01) to a loss of 0.025 units. Substitution of half the added Phe with Tyr lowered (P<0.05) milk and milk lactose yields while further lowering (P<0.01) the BCS loss to 0.080 units/28 d. While differences among diets in plasma AA concentrations were small, adding Phe to the HCM diet increased (P=0.05) plasma Phe and Ala (P=0.02), but plasma Phe only tended (P=0.09) to decline when Tyr partially replaced Phe to create the HCM+PT diet. Contrary to expectations based upon prior studies, increased CM inclusion from 120 to 170 g/kg DM only modestly decreased overall animal performance. While it is clear that supplementation of Phe, or Phe plus Tyr, to the HCM diet was not necessary, the 2 unexpected and substantive negative effects of Phe or Phe plus Tyr on overall animal performance suggests that the bioactivity of these AA is highly important, while highlighting the risks of supplementing AA that are not required.

Impacts of substitution of canola meal with soybean meal, with and without ruminally protected methionine, on production, reproduction and health of early lactation multiparous Holstein cows through 160 days in milk

“…Blood AA concentrations were similar to Gauthier et al (2019) and mostly within 'normal' ranges for high producing Holstein dairy cattle (Swanepoel et al, 2018). Only glutamine was lower than in Swanepoel et al (2016), but comparable to values later reported by our group (Swanepoel and Robinson, 2019a), while arginine appeared almost 2x higher than levels reported previously.…”

“…The purpose of compositing urine and fecal samples into these cow composite groups was to support the assumption that the chemical composition of the TMR consumed by the composite groups was represented by the TMR sampled for chemical analysis (Swanepoel et al, 2018).…”

Phenylalanine and valine differentially stimulate milk protein synthetic and energy-mediated pathway in immortalized bovine mammary epithelial cells

“…Thus, further analyses were performed to investigate the effects of PHE or VAL on protein synthesis-related responses and energy-mediated cellular signaling in MAC-T cells. When high milk-producing Holstein cows fed a rumen protected form of PHE, little or no change in body conditions score were observed and there is either a tendency towards a decrease or no change in true milk protein yield compared to control group [14][15][16]. However, our study showed a significant increase in concentrations of protein in both the cultured medium and within cells after PHE treatment ( Fig.…”