Effect of Increasing Protein and Fat Inclusion in the Diets of Beef Cows during Gestation and Lactation on Progeny Performance, Carcass Characteristics, and Plasma Nonesterified Fatty Acids

This study was conducted to evaluate the effects of increasing CP and fat inclusion in the diets of Angus x Simmental cows during late gestation through mid lactation on progeny feedlot performance, carcass characteristics and plasma NEFA concentration. Forty-eight cows (610 ± 16.8 kg BW), pregnant with male progeny, were allotted by BW and BCS to 4 treatments arranged in a 2 x 2 factorial, with 2 CP (11.9 and 17.1%) and 2 fat (2.0 and 4.8%) concentrations in the diet DM. Treatment diets were formulated to be isocaloric, and were fed to cows in individual pens for 178 d. The average calving date was on d 85 ± 7.2 from treatment start. After the treatment period, cow-calf pairs were placed on pasture and managed as one group until weaning (d 279). Steers were then transitioned to a common backgrounding diet, fed until d 414 (329 d of age) and placed in an indoor feedlot in individual pens. Steers were fed a feedlot diet for 142 d composed of 57% dry-rolled corn, 22% dried distillers grains with solubles, 10% corn silage, 5% rye silage, and 6% vitamin/mineral supplement in the diet DM. Jugular blood samples were collected at the beginning and end of the feedlot period to determine plasma NEFA concentration using a commercial kit. Steers were slaughtered at a target BW of approximately 648 kg and carcass characteristics were determined after a 24-h chill. Data were analyzed using the MIXED procedure of SAS. No interactions among dietary CP and fat concentrations were observed (P≥0.31). Initial and final BW, as well as ADG, DMI, and gain:feed of the steers throughout the feedlot period were not affected by CP (P≥0.26) or fat (P≥0.70) in the maternal diet. Similarly, increasing CP or fat inclusion in the diets of dams had no effects (P≥0.25 and P≥0.17 for CP and fat, respectively) on HCW, dressing, fat thickness, LM area, and yield grade of progeny carcasses. Moreover, plasma NEFA of steers at the beginning and end of the feedlot period were not affected by the increasing inclusion of CP (P≥0.36) or fat (P≥0.23) in the maternal diet. In summary, increasing CP or fat inclusion in the diets of cows during late gestation through mid lactation had no long-term effects on performance, carcass characteristics, and plasma NEFA concentrations of their male progeny.