Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: May 15, 2005
Publication Date: June 15, 2005
Citation: Grings, E.E., Roberts, A.J., Geary, T.W. 2005. Milk yeild of beef heifers from three calving systems. Journal of Animal Science 83(Suppl 2):122 (#90). Interpretive Summary: same as abstract
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.