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ARS Home » Plains Area » Miles City, Montana » Livestock and Range Research Laboratory » Research » Publications at this Location » Publication #185043
Title: MILK YIELD OF BEEF HEIFERS FROM THREE CALVING SYSTEMS

Author
item Grings, Elaine
item Roberts, Andrew
item Geary, Thomas

Submitted to: Western Section of Animal Science Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 5/15/2005
Publication Date: 6/15/2005
Citation: Grings, E.E., Roberts, A.J., Geary, T.W. 2005. Milk yield of beef heifers from three calving systems. Western Section of Animal Science Proceedings. 56:131-134

Interpretive Summary: Milk yield of the dam is a major determinant of growth rate in beef calves. Forage quality within rangeland systems can affect growth rate of calves through influences on the milk yield of dams and the quality of the forage portions of a calf’s diet. Adjusting calving time of beef cows from late winter through late spring impacts the quality of forage available for milk production and growth of beef cattle in the Northern Great Plains. This 2-year study evaluated the milk yield in a 190-d lactation of heifers born and raised within three calving systems and the impact on growth of their calves. Calving dates were late January to late February (Feb calving), mid-March to mid-April (Apr calving), and mid-May to mid-June (Jun calving). During the period of milk production measurements heifers were maintained primarily on native rangeland. Milk production was measured by weigh-suckle-weigh techniques at an average of 20-, 38-, 55-, 88-, 125-, 163- and 190-d of lactation. Total milk yield did not differ between heifers in Feb and Apr systems, yet both differed from Jun. However, this relationship was affected by year. In 2002, Jun heifers produced more, whereas in 2003 they produced less milk than heifers in other calving systems. The average daily gain of calves for the three systems related well to the total milk yields. Day of peak lactation differed among calving systems with heifers in the Feb system peaking later than those heifers from other systems. Average calendar day of peak lactation was May 4 for the Feb system, May 31 for the Apr system, and July 19 for the Jun system. Day of peak did not differ among years even though forage quality patterns differed between years. Season of calving and its associated management affects time and amount of milk yield in heifers, corresponding to varied weight gains in their calves. Understanding the impacts of calving date on amounts and patterns of milk production can aid in developing management systems to best match nutrient needs of cow-calf pairs in different calving systems.

Technical Abstract: In a 2-yr study, first-calf heifers from three calving systems were used to study milk yield throughout a 190-d lactation. Calving occurred in late January to late February (Feb calving), mid-March to mid-April (Apr calving), and mid-May to mid-June (Jun calving). Milk production was measured by weigh-suckle-weigh technique on seven dates for each herd. Average days in milk at measurement were 20-, 38-, 55-, 88-, 125-, 163- and 190-d. Milk yield for the entire lactation period was calculated as area under the curve by trapezoidal summation. Total milk yield over the 190-d lactation exhibited a calving system x year interaction (P < 0.001). Total yield did not differ between heifers in Feb and Apr systems, yet both differed from Jun. In 2002, Jun heifers produced more (P < 0.05), whereas in 2003 they produced less (P < 0.01) milk than heifers in other calving systems. The ADG of calves for the three systems related well to the total milk yields. The Feb calves showed an increased (P < 0.05) rate of gain in 2003 compared to 2002 and Jun calves grew more slowly (P < 0.01) in 2003 than 2002. Milk yield at peak lactation was affected (P < 0.001) by calving system and showed a calving system x year interaction (P < 0.01). In 2002, peak milk yield did not differ between Feb and Apr heifers, and both were less (P < 0.01) than Jun heifers. In 2003 peak milk yield in Apr and Jun heifers did not differ and both tended to be greater (P < 0.10) than Feb heifers. Day of peak lactation differed among calving systems (P < 0.001) with heifers in the Feb system peaking later (P < 0.01) than those heifers from other systems. Average date of peak lactation was May 4 for the Feb system, May 31 for the Apr system, and July 19 for the Jun system. Date of calving affects milk yield of heifers and ADG of their calves while grazing Northern Great Plains rangelands.