Milk Expected Progeny Difference and Its Effect on
Reproductive Performance of Mature Beef Cows from Angus and Polled
S. Erat and D.S. Buchanan
Story in Brief
The objective of this study was to evaluate the reproductive
performance of mature beef cows sired by High and Low Milk EPD Angus and Polled
Hereford bulls. Cows were produced
through the mating of these bulls to Angus x
Key Words: Beef Cattle, Reproduction, Expected Progeny Difference
Introduction
The primary objective of a commercial cow-calf enterprise is the production of calves that are heavy and high quality at weaning. Therefore, profitability of a cow-calf enterprise depends on the percentage of cows in the herd that consistently calve every year. Cows with high genetic merit for maternal ability should have heavy calves at weaning due to milking ability of the cow. This additional milk may cause some cost in cow weight and condition which may have a negative effect on reproductive performance. Previous studies (Buchanan et al., 1993, 1995, 1996a; Gosz and Buchanan, 1998; Minick et al., 1999; Buchanan and Stutts, 2001) have shown that the Milk EPD is an effective tool for increasing calf weaning weight but there is a cost in cow body condition. The objective of this study was to examine the reproductive performance of mature beef cows sired by High and Low Milk EPD Angus and Polled Hereford bulls.
Materials and Methods
All cows in this study were from the
Cows were artificially inseminated for a period of approximately 55 d and then turned out with crossbred bulls for 20 d clean up period. Cows that were not pregnant after a 75-d breeding season were moved to the opposite breeding season. Cows failed to conceive in two consecutive breeding seasons were culled from the herd.
Calving interval, calving date, calving percentage, and calving rate were calculated. Calving interval was calculated as the number of days between subsequent calvings without regard to the season. Calving date was calculated as the number of days following the beginning of the calving season. Calving percentage was calculated as the proportion of cows that gave birth to a calf (alive or dead) during the same calving season one year following their previous calf. Calving rate was calculated as the proportion of cows that were bred and that also gave birth to a calf.
The data were analyzed using least squares. Terms included in the statistical models were cow sire breed, Milk EPD level, year, season, sex of calf, age of cow within year and interactions among those variables.
Results and Discussion
Least squares means for calving interval, calving date, calving percentage and calving rate are given in Table 1. Breed was not significant for calving date (P>.7) and for calving interval (P>.3). Milk EPD level had also no significant effect on calving date (P>.2) and calving interval (P>.3). Breed and Milk EPD level had no significant effect (P>.3) on both calving percentage and calving rate. These variables (calving interval, calving date, calving percentage and calving rate) do not give a whole picture of reproductive performance of cows alone. Together, they indicate if cows calve on schedule and if cows are calving at different point in the calving season or are delayed sufficient enough to have their next calf the following season. Even though none of these four variables were different (P>.2) in this study, cows sired by High Milk EPD bulls had slightly lower calving percentage and calving rate, longer calving interval, and later birth dates than cows sired by Low Milk EPD bulls. Thus, they indicate a decline in reproductive performance in conjunction with the loss in condition score reported previously by Buchanan et al. (1993, 1995, 1996a, 1996b), Gosz and Buchanan (1998), Minick et al. (1999), and Buchanan and Stutts (2001).
|
Table 1. Least squares means and standard errors for calving interval (CI), calving date (CD), calving percentage (CP), and calving rate (CR) |
|||||
|
Breed |
Level |
CI (days) |
CD (days) |
CP (%) |
CR (%) |
|
Angus |
High |
383.11 ± 5.60 |
34.50 ± 3.21 |
82.60 ± 3.82 |
90.80 ± 2.77 |
|
Angus |
Low |
379.47 ± 5.12 |
32.59 ± 3.16 |
90.55 ± 3.46 |
93.64 ± 2.61 |
|
P. Hereford |
High |
379.41 ± 6.40 |
33.27 ± 3.26 |
87.95 ± 4.42 |
89.47 ± 3.37 |
|
P. Hereford |
Low |
373.21 ± 5.39 |
32.84 ± 3.17 |
84.18 ± 3.52 |
89.94 ± 2.63 |
Literature cited
Buchanan, D.S. et
al. 1993.
Buchanan, D.S.
et al. 1995.
Buchanan, D.S. et al. 1996a.
Buchanan, D.S. et al. 1996b.
Gosz, R.J. and
D.S. Buchanan. 1998.
Minick, J. et al. 1999.
Buchanan,
D.S. and K.J. Stutts. 2001.
Acknowledgements
The authors thank the numerous breeders who donated semen for this study.
Copyright 2005 Oklahoma Agricultural Experiment Station
Authors
Erat, S. – Assistant Professor, Department of Animal Husbandry and Animal Nutrition, Faculty of Veterinary Medicine, Kirikkale University, Yahsihan, Kirikkale 71451, Turkey
Buchanan, D.S. – Professor