PS3-17. Sexual Dimorphism of Supplementation with Rumen-protected Methionine in Early Gestation in Beef Cattle Systems – Postweaning Effects.

Abstract

Maternal supplementation with rumen-protected methionine (RPM) may improve embryo development and calf performance when fed during early gestation. Previous data from our group indicated male calves from RPM-supplemented dams during the periconceptional period higher birthweight compared to control calves, with no differences in females, suggesting a sexually dimorphic response. We hypothesize that supplementing beef cows with RPM during the periconceptional period will influence embryo development, resulting in larger and heavier male calves with no differences in females. In this study, lactating beef cows 58 ± 18 days postpartum were randomized to 454 g/d corn gluten with 15 g/d RPM (RPM; n = 124) or not (CON; n = 126) from days −7 to 7 relative to timed-artificial insemination (TAI = day 0). Supplementation used an automated feeder allowing tracking of intake, and only animals with adequate consumption remained in the study (CON; n = 69; RPM; n = 75). Transrectal ultrasonography was conducted for pregnancy diagnosis, and only pregnant cows (CON; n = 27; RPM; n = 29) remained in the study. After calving, calves were weighed and identified (CON; n = 23; RPM; n = 24). After weaning, calves were measured monthly (weight, body length, hip height, and heart girth) for three months. After this, carcass ultrasonography was performed and calves entered a 56-day feed efficiency trial following a 15-day adaptation period. After completion of the trial, a second carcass ultrasonography was performed. Data were analyzed using MIXED procedure of SAS (SAS Institute), with treatment, sex, and their interaction as fixed effects, and group as random effect, AR(1) covariance structure was used for repeated measurements. Body weight, hip height, body length, and heart girth were not affected by treatment or treatment × sex interaction (P > 0.05). A sex effect was detected for body weight (P = 0.046), hip height (P = 0.014), and body length (P = 0.028), being greater in males (Table 1). Average daily gain tended to differ by treatment (P = 0.079) and sex (P = 0.054), with CON calves and males presenting greater gains; no treatment × sex interaction was detected (P = 0.87). Residual feed intake (P = 0.93) was not affected by treatment, sex, or interaction (P > 0.05). Carcass ultrasonography ribeye area, intramuscular fat, subcutaneous fat thickness, rump fat thickness and yield ratio were not affected by treatment or treatment × sex interaction (P > 0.05). Sex effects were detected for intramuscular fat (P = 0.004), fat thickness (P = 0.017), rump fat (P = 0.021), and yield ratio (P = 0.031), being greater in females (table 2). These preliminary results suggest that RPM supplementation does not affect postweaning morphometric and carcass quality traits, ongoing analysis will determine gene expression and DNA methylation.

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