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ARS Home » Plains Area » Miles City, Montana » Livestock and Range Research Laboratory » Research » Publications at this Location » Publication #293818

Title: Fall pasture quality for cows in mid-pregnancy has minimal effects on offspring growth

Author
item GRINGS, ELAINE - South Dakota State University
item Roberts, Andrew

Submitted to: Western Section of Animal Science Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 5/15/2013
Publication Date: 6/21/2013
Citation: Grings, E.E., Roberts, A.J. 2013. Fall pasture quality for cows in mid-pregnancy has minimal effects on offspring growth. Western Section of Animal Science Proceedings. 64:262-265.

Interpretive Summary: The impact of pasture quality during the autumn grazing period on offspring of cows calving in late winter was studied over 4 years. Each year, between 26 and 50 cows, with an average calving date of February 12, were allocated to one of two grazing treatments from about September 28 to November 19; cows grazed either pastures of seeded forage (average CP = 10.2% DM basis) from which a harvest of hay had been removed followed by flood irrigation in August or native rangeland pastures (average CP = 6.7%). Weight change during this grazing period was similar for cows in the 2 treatments (143 vs. 134 lbs. for seeded vs. native forage). At the end of the grazing treatment, cows were moved to drylots and fed a corn silage-based diet until calving. After calving, cows were fed hay and/or supplement until native rangeland forage was adequate to support production. Pre-weaning growth, weaning weights, and post weaning growth of calves did not differ due to type of pasture grazed in autumn. However, pre-weaning weight gain of calves was positively related (r = 0.38) to weight gain of cows during the grazing period, but this was not affected by the grazing treatment. Weight gain of cows during grazing was negatively correlated (r = -0.36) to weight of cows at the beginning of the grazing period. This likely indicates that heavier cows had higher nutritional demands for maintenance and gained less during grazing. Subsequently, these cows may have had lower energy reserves for milk production and pre-weaning calf growth. Retention of female offspring in the reproductive herd over the several years following grazing appeared to be lower for daughters from cows that grazed native rangeland in autumn. This difference in retention resulted in less weight of calf produced per year over the lifetime of the female progeny of cows grazing native rangeland compared to those of cows grazing seeded pasture. In conclusion, cows on pastures of differing quality selected diets that allowed them to stay in positive nutrient balance throughout the grazing period. Therefore, nutritional quality of pastures grazed by pregnant late winter calving beef cows for 2 months in autumn did not affect weights or growth of offspring to 1 year of age. However, it appears that access to higher quality forages during this period maybe beneficial for retention of the female offspring kept for replacements.

Technical Abstract: The impact of pasture quality during the autumn grazing period on offspring of cows calving in late winter was studied over 4 years. Each year, between 26 and 50 cows, with an average calving date of February 12, were allocated to one of two treatments replicated in two pastures for the autumn grazing period. Cows grazed either pastures of seeded forage (26 ha each; average CP = 10.2% DM basis) from which a harvest of hay had been removed followed by flood irrigation in August or native rangeland pastures (71 or 90 ha; average CP = 6.7%). Cows grazed from about September 28 to November 19 at which time they were moved to drylots and fed a corn silage-based diet until calving. After calving, cows were fed hay and/or supplement until native rangeland forage was adequate to support production. Analysis of variance was conducted using a General Linear Models procedure to evaluate year, treatment and year by treatment interactions with age of dam and birthdate used as covariates and pasture within treatment as the experimental unit. Pre-weaning growth and 190-d adjusted weaning weights of calves did not differ due to type of pasture grazed in autumn. Pre- weaning ADG and 190-d adjusted weaning weight were 1.10 ± 0.01 kg/d and 245.8 ± 2.0 kg for heifers and 1.16 ± 0.01kg/d and 260.4 ± 2.1kg for steers. However, a tendency (P < 0.08) for a treatment by year interaction was observed for preweaning ADG for heifers. No differences in post-weaning ADG or weight at about one year of age were observed for cow grazing treatment for either heifers (P = 0.55, P = 0.67) or steers (P = 0.27, P = 0.22). Heifers and steers gained 0.59 ± 0.01 and 0.96 ± 0.01kg/d, respectively post-weaning. At 360 days of age, heifers weighed 342 ± 3.1 kg and steer weighed 416 ± 2.9 kg. Nutritional quality of pastures grazed by pregnant late winter calving beef cows for two months in autumn did not affect weights or growth of offspring to one year of age.