Abstract
To determine the effects of leucine supplementation on body weight (BW), tissue mass, nutrient digestibility, the concentration of serum amino acids (AAs) and metabolites, and protein abundance of elongation initiation factor 4E (eIF4E) in skeletal muscle, 23 Holstein bull calves (43. 3 ± 1.16 kg; 11.3 ± 0.57 days of age) fed milk replacer at 2.5% of body weight (BW; dry matter basis) were used in a randomized complete block design. Leucine was supplemented at 0, 0.4, 0.6, or 0.8 g Leu/kg BW per day for 28 d. Data were analyzed using the MIXED procedure of SAS. Leucine supplementation did not affect calf BW (P = 0.73), and digestibility of nitrogen (P = 0.21), organic matter (P = 0.28), and dry matter (P = 0.28). Masses proportional to BW of the pancreas (P = 0.04), omasum (P < 0.01), and spleen (P = 0.01) were quadratically affected by treatment where tissue mass decreased at 0.4 g Leu/kg BW and increased at 0.6 and 0.8 g Leu/kg BW. Semitendinosus mass proportional to BW tended (P = 0.07) to be quadratically affected, as tissue mass increased at 0.4 g Leu/kg BW, and decreased at 0.6 and 0.8 g Leu/kg BW. Serum Leu concentration increased linearly (P = 0.002; day × time × treatment) across days and after feedings with increased supplemental Leu. Increasing supplemental Leu linearly decreased serum Ala (P < 0.01), Arg (P = 0.04), Ile (P = 0.02), Met (P < 0.01), and Pro (P = 0.05) concentrations, and quadratically affected serum Glu (P = 0.04) and Lys (P = 0.03) concentrations where serum Glu and Lys concentrations were decreased at 0.4 g Leu/kg BW and increased at 0.6 and 0.8 g Leu/kg BW. There was no effect of treatment on protein abundance of eIF4E in semitendinosus or longissimus dorsi. These data indicate that supplemental Leu did not influence ADG and nitrogen retention in calves fed milk replacer. However, changes in serum AA concentrations and tissue masses proportional to BW suggest that supplementation of Leu at lower levels could increase the use of AA for non-visceral tissue growth.
Highlights
IntroductionMilk or milk replacer is the primary component of the diet for calves
During early life, milk or milk replacer is the primary component of the diet for calves
Mass of omasum (g and g/kg body weight (BW)) responded quadratically (P = 0.01) to supplemental Leu treatment where Leu supplemented at 0.4 g/kg BW decreased tissue mass compared with other treatments
Summary
Milk or milk replacer is the primary component of the diet for calves. Soberon et al (2012) reported that increased pre-weaning plane of nutrition in Holstein heifers during the pre-weaning period was associated with an increase in future milk production. These results suggest a developmental programming effect on long-term productivity. Skeletal muscle protein synthesis and growth is rapid in the pre-weaning period (Wray-Cahen et al, 1998; Zheng et al, 2019) and requires adequate amino acid (AA) supply. Pre-weaned lambs are sensitive to dietary imbalances of AA (Rogers and Egan, 1975), and oversupply of non-limiting AA results in increased catabolism leading to a delay in muscle growth. AA supplementation strategies should be explored to improve preweaning growth, and potentially lead to improvements in lifetime productivity
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