Summary
Records collected from 1997 to 2014 were analyzed to evaluate the eff ects of dam age on off spring productivity. Steer calves born from young mothers (2 and 3 yr old dams) had lighter carcasses with more carcasses grading Choice and upper 2/3 Choice. Th e calving performance and reproductive performance in the second breeding season for heifer calves born from fi rst calving dams were the lowest compared with heifers born from multiparous dams. A quadratic eff ect of dam age on off spring performance was observed; as dam age increased, off spring performance increased, until dam age reached 7 to 8 yr and then off spring performance decreased.
Introduction
It is well accepted fi rst calving heifers and old cows are less productive than middle age cows. Beef breed associations and the Beef Improvement Federation Guidelines (2010) recommend adjusting the birth and weaning weight of calves contingent upon dam age. However, most of the studies limit their comparisons to primiparous vs. multiparous females and researchers concentrate on dam performance or off spring performance only in the pre- weaning phase. Few studies have evaluated the eff ects of dam age on off spring productivity later in their lives, especially for heifer calves. Th is study evaluated the eff ects of dam age at calving on male calf performance from birth to slaughter and female calf productivity from birth through her second breeding season.
Procedure
Data was collected from a composite Red Angus × Simmental herd from the Gudmundsen Sandhills Laboratory (GSL),
Whitman, NE from 1997 to 2014 for heifer calves (n = 1,524) and from 2003 to 2014 for steer calves (n = 1,195).
Breeding protocol
From 1997 to 2002, cows and heifers were exposed to a natural service breeding season for 60 d at a bull to female ratio of 1:25. From 2003 to 2014, females were exposed to bulls for 45 d at a bull to female ratio of 1:25 and a single injection of PGF2α was administered i.m. 108 h aft er placement with bulls. Pregnancy diagnosis was performed via transrectal ultrasonography approximately 45 d aft er the breeding season.
Culling and replacement
Cows and heifers were culled when they failed to become pregnant; cows were also culled for advanced age or health issues. First calving heifers replaced culled cows. All replacement heifers were born and developed at GSL.
Off spring performance
Heifer calves
Performance parameters evaluated included: birth weight, adjusted 205 d weaning weight, pre- breeding BW, BW and BCS at pregnancy diagnosis, BW and BCS at calving, and BW and BCS at weaning of their fi rst calf. Reproductive performance parameters include pubertal status and pregnancy rate for their fi rst and second breeding seasons. Pubertal status was determined by progesterone concentration measured in 2 blood samples taken 10 d apart prior to the fi rst breeding season.
Steer Calves
Performance parameters evaluated included: birth weight, adjusted 205 d weaning weight, BW at slaughter, HCW, ADG from birth to weaning, and ADG from weaning to slaughter. At slaughter,
marbling score, fat thickness, ribeye area, and yield grade were measured.
Statistical analysis
Data were analyzed using PROC GLIMMIX of SAS 9.4 (SAS Inst., Inc., Cary, NC). Th e model includes the fi xed eff ect of dam age, and random eff ects of yr and treatment applied to dam and off spring due to other experiments occurring simultaneously to this study. Means were adjusted using Julian birth date as a covariate. Orthogonal contrasts were used to compare primiparous and multiparous females and also to evaluate the linear and quadratic eff ects of dam age on off spring productivity.
Results
Th e results for the heifer calves are presented in Table 1. Compared with multiparous, primiparous- born heifer calves had lower birth BW, adjusted 205 d weaning weight, pre- breeding BW and pregnancy diagnosis BW (P < 0.05). Th ere was a linear and quadratic relationship (P < 0.05) of dam age on birth BW and adjusted 205 d weaning weight. Th e same pattern is observed for steer calf birth BW and adjusted 205 d weaning weight (P < 0.05, Table 2). Final BW and HCW were greater for middle age steer calves (Table 2) (primiparous vs. multiparous contrast and quadratic eff ect, P < 0.05). As dam age increases, off spring BW at diff erent phases also increases until the dam is 7 to 8 yr old and then decreases.
A lower percentage of heifers born from primiparous dams were pubertal prior to the breeding season compared with heifers born from multiparous dams (P < 0.01). Th ere was a linear tendency (P = 0.06) of dam age aff ecting the percentage of heifers pubertal prior to the breeding season, heifers born from young dams tended to have a lower cycling rate compared with heifers from older dams, but no diff erence was observed on pregnancy rates in the fi rst breeding season (P > 0.10).
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Source: Nebraska Beef