Effects of Timing of Weaning in a Fall-Calving System on Performance of Beef Cows and Their Progeny
M.D. Hudson, J.P Banta, D.S. Buchanan, and D.L. Lalman
Story in Brief
Predominantly Angus beef cows were used in two consecutive years to investigate the effects of timing of weaning on cow body weight and condition, reproductive performance, milk production, and calf performance of fall-calving beef cows and their progeny. Cows were assigned to two weaning treatments: (1) Traditional weaning in mid-April at approximately 210 d of age (Treatment=APRIL) and (2) Late weaning in mid-July at approximately 300 d of age (Treatment=JULY). Performance data were analyzed by number of years on trial: (1) Cows/calves in their first year on trial (YOT=1) and (2) Cows/calves in their second year on trial (YOT=2). No statistical differences in performance were noted for YOT=1 cows, although APRIL cows were numerically fleshier than JULY cows at the July weaning date. In their second year on trial, APRIL cows were 83 lb heavier and .8 units fleshier at the July weaning date and .7 units fleshier at pre-calving than JULY cows. Percent pregnant did not differ between treatments for YOT=1 or YOT=2. Progeny of YOT=1 cows did not differ significantly for any pre-weaning or weaning traits measured. However, progeny of YOT=2 APRIL cows were born 8 d earlier in the calving season and were heavier throughout the pre-weaning period. Despite numerically lighter weights in April, progeny of JULY cows out-gained APRIL calves from April to July and were significantly heavier in July in YOT=2. These data indicate that under normal conditions, later weaning fall-born calves results in heavier weaning weights without depressing cow reproductive performance; however, as evidenced by the differences in performance from YOT=1 to YOT=2, there appears to be a cumulative effect of this practice resulting in cows rebreeding later in the breeding season.
Key Words: Fall-Calving, Cows, Timing of Weaning, Performance
Introduction
This practice appears to have a positive influence on enterprise profitability due primarily to heavier weaning weights of older calves. However, the extended lactation period may result in thinner conditioned cows at the beginning of the calving season. Cow body condition score (BCS) at calving is an important factor affecting the length of the post-partum interval (PPI) and pregnancy rates (Wiltbank et al., 1964; Selk et al., 1988). The greater the BCS at parturition, the shorter the interval to first estrus (Richards et al., 1986; Houghton et al., 1990).
Our objective is to elucidate the effects of timing of weaning on performance of fall-calving beef cows and their progeny.
Materials and Methods
Cattle and Treatments. This study
was conducted at the
Management and Weighing Procedures. In both years, in mid-April (yr 1, April 20, 2004; yr 2, April 19, 2005; d=0) after a 16-h shrink, all cows and calves were dewormed using Ivomec Plus. Cow body weights and BCS and calf weights were recorded.
APRIL calves were separated from their dams and weaned using a fenceline weaning system. APRIL calves were maintained in drylot for 10 d post-weaning and were given ad libitum access to bermudagrass hay and water and were fed a 20% crude protein supplement at a rate of 4 lb/hd per day. On d-10 calves were placed on excellent quality native grass pasture (burned in early April) at a stocking rate of approximately 3 ac per calf.
In mid-July (July 13, 2004, yr 1; July 12, 2005, yr 2; d=84), after a 16-h shrink, cow body weights and BCS and calf weights were recorded for both treatments. JULY calves were separated from their dams and weaned using the fenceline weaning system. JULY calves were managed post-weaning the same as APRIL calves. Shrunk calf weights were recorded for both APRIL and JULY calves on d-105.
Cow weights and BCS were recorded at pre-calving in late-August, at pre-breeding in late November, at pre-green up in late March (yr 1)/early April (yr 2), and at both weaning dates. Cows were pregnancy checked at the pre-green up weigh date. All open cows remained on the study until the July weaning date and were then removed from the study.
In both years, cows were artificially inseminated for a 3-wk period before clean-up bulls were turned in for an additional 6 wk.
Statistical Analysis
Cow and calf performance data were analyzed using the MIXED model procedure of SAS. Interactions and covariates that were non-significant (P>.20) for the F-statistic were removed from the model. Cow performance, calf weaning performance, and calf pre-weaning performance data were analyzed separately by number of years on trial: (1) Cows/calves in their first year on trial (YOT=1) and (2) Cows/calves in their second year on trial (YOT=2). Data presented in tables are the least square means.
Cow analyses 1 and 2 included in the model terms for weaning treatment and cowage. Both calf analyses 1 included in the model terms for weaning treatment, cowage, sex, birth date, and birth weight. Calf analyses 2 included in the model terms for weaning treatment, cowage, sex, and breed of sire. For analyses 1, year and all possible interactions were considered random variables. For analysis 2, year was not different, therefore a random variable was not included in the model.
Results and Discussion
Performance of Cows and Their Progeny in Their First Year on Trial. Data in Table 1 are pooled performance results for cows in their first year on the trial in yr 1 (from April 2004 to April 2005) and in yr 2 (from April 2005 to April 2006). By design, initial cow body weight and BCS did not differ significantly between treatments. APRIL cows tended to have higher BCS in both July and at pre-calving in late August (P=.13 and .14, respectively). Differences in subsequent calf birth weight and cow pregnancy rate were not statistically significant.
Pooled performance data for calves nursing cows when the study was initiated (YOT=1 for their dams) are shown in Table 2. JULY calves tended to weigh more than APRIL calves in July (P=.17), although August weights and averaged daily gain differences were not statistically significant.
These weaning treatments have potential long term influence on cow and calf performance. Therefore, the performance of the cows and their calves during the production cycle following execution of the treatments are presented. Table 3 includes performance data for calves born to cows after the APRIL and JULY weaning treatments (YOT=1). No statistical differences were observed for any traits measured.
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Table 1. Effect of weaning treatment on cow performance for cows in their first year on trial (YOT=1). |
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Table 2. Effect of weaning treatment on performance of calves reared by cows in their first year on trial (YOT=1). |
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Table 3. Effect of weaning treatment on performance of calves born to cows after weaning treatments were applied (YOT=1). |
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Performance of Cows and Their Progeny in Their Second Year on Trial. Table 4 presents cow performance data for YOT=2 from April 2005 to April 2006. April weight and BCS did not differ significantly between treatments. However, at the July weaning date, APRIL cows were 83 lb heavier and .8 units BCS greater than JULY cows. Similarly, at pre-calving, APRIL cows were 73 lb heavier and .7 units BCS greater than JULY cows. APRIL cows tended to calve earlier than JULY cows (9.5 d, P=.16). Calf birth weight did not differ between treatments (81 vs 82; P=.74). No statistical differences were recorded for pregnancy percent between treatments.
Shown in Table 5 are performance data for calves reared by dams in their second year on trial. Progeny of JULY cows outperformed APRIL calves in the 84-d period from April to July (35 lb) and overall from April to August (25 lb).
Pre-weaning performance data for calves born to cows after weaning treatments were applied the second year (YOT=2) are shown in Table 6. APRIL calves tended (P=.08) to be heavier in April, outweighing JULY calves by 34 lb. APRIL calves also tended (P=.17) to out-gain JULY calves from birth to April.
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Table 4. Effect of weaning treatment on cow performance for cows in their second year on trial (YOT=2). |
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Table 5. Effect of weaning treatment on performance of calves reared by cows in their second year on trial (YOT=2). |
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Table 6. Effect of weaning treatment on performance of calves born to cows after weaning treatments had been applied the second year (YOT=2). |
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Implications
Delaying weaning until July dramatically increased weaning weights during this 2-yr study due to forage quality and availability during the extended lactation period. However, substantial cow weight gain and gain in cow body condition are sacrificed when calves are weaned late. This practice may eventually lead to reduced reproductive performance of the cow/calf enterprise. Additionally, one would expect cow and calf performance to differ under varying conditions such as prolonged heat and/or drought. This experiment will be continued and expanded to measure feed intake during early lactation, blood sampling to determine cyclicity at the beginning of the breeding season, and to include economic analysis.
Literature Cited
Houghton, P. L. et al. 1990. J. Anim. Sci. 68:1438-1446.
Richards, M. W. et al. 1986. J. Anim. Sci. 62:300-306.
Selk, G. E. et al. 1988. J. Anim. Sci. 66:3153-3159.
Wiltbank, J. N. et al. 1964. J. Anim. Sci. 23:1049.
Acknowledgments
The authors would like to thank Duane Williams, Joe Steele, and Jared Jones for management of the cowherd throughout the study and assistance with data collection.
Copyright 2006 Oklahoma Agricultural Experiment Station.
Authors
Hudson, M.D. – Graduate Student
Banta, J.P. – Former Graduate Student
Buchanan, D.S. – Professor
Lalman, D.L. – Associate Professor