Direct and correlated responses to selection for yearling weight onreproductive performance of Nelore cows1

Abstract

Data from a selection experiment for growth carried out in Brazil were analyzed in order to evaluate the direct responses on yearling weight (YW) and the correlated responses on the size and reproduction traits of cows. The experiment was started in 1976, and in 1980 three lines of Nelore cattle were established: selection (NeS), traditional (NeT), both selected for higher YW, and control (NeC), selected for mean YW. The NeT was an open line that eventually received bulls from other herds. Yearling weight records for animals born from 1978 to 1998 and yearling hip height (H550) offemales born from 1985 to 1998 were analyzed by fitting an animal model in order to obtain the genetic trends. The means for weight, height, and body condition score at the start of the breeding season, days to calving, and calving success of cows born from 1993 to 1996 (pertaining to the third to fourth generations of selection) were compared between the selected (NeS and NeT) and control lines. The genetic trends obtained after 16 yr for YW were 1.7 +/- 0.2, 2.3 +/- 0.2, and -0.1 +/- 0.1 kg/yr for males and 1.9 +/- 0.2, 2.4 +/- 0.2, and -0.1 +/- 0.1 kg/yr for females, for the NeS, NeT, and NeC lines, respectively. Corresponding values for H550 were 0.25 +/- 0.03, 0.24 +/- 0.04 and -0.04 +/- 0.03 cm/yr for females. Heifers and cows from NeS and NeT were 19% and 15% heavier and 4% taller at the start of the breeding season than those from NeC. No significant differences between selected (NeS and NeT) and control females were detected for body condition scores and for reproductive performance. The results indicate that selection for body weight promoted high and consistent weight and height responses both at the yearling and later ages, without compromising the reproductive performance of the cows with respect to days to calving and calving success.

Genetic variability in calving success in Aberdeen Angus cows under extensive recording

“…Repeatability models (e.g. Mercadante et al, 2003) assume a genetic correlation of one among calving opportunities, but our results do not support a repeated measures model. Uncertainty in all correlations was large, however.…”

“…Recently, heifer pregnancy status and the outcome of subsequent rebreeding have attracted interest (Evans et al, 1999;Doyle et al, 2000;Eler et al, 2004). Calving success (CS) has been studied as well (Meyer et al, 1990;Mercadante et al, 2003;Donoghue et al, 2004d). Rust and Groeneveld (2001) summarised advantages and disadvantages of different component traits.…”

Long-term selection experiment with Afrikaner cattle 3. Selection applied and response in calf growth traits

“…Selection experiments in beef cattle have been mainly concerned with improvements in growth traits, with published reports of 1.8 to 6.3 generations of selection (Mrode, 1988b;Baker et al, 1991;Koch et al, 1994;Parnell et al, 1997;Razook et al, 1998;Mercadante et al, 2003, Koch et al, 2004Pereira et al, 2008). However, Mrode (1988a) noted that many earlier experiments suffered from inadequate designs with respect to population size and levels of inbreeding.…”

Productive efficiency of cows primiparous aberdeen angus of the body size and milk production levels

“…Heavier cows produce calves with higher pre-weaning growth rates and consequently heavier at weaning (MERCADANTE et al, 2003). However, when the environmental and nutritional adversity post-calving are limiting, their high maintenance costs may compromise milk production and the performance of calves (CERDÓTES et al, 2004), or, in the case of the present study, this may be due to the fact that they are primiparous and still growing, with a greater nutritional requirement when compared with adult cows .…”

“…These body weight losses by the cows are due to the greater requirement of the cow-calf set during lactation, which can increase by 85-90% at third month up to 100 to 120% by the fifth month of lactation (ROVIRA, 1996). The similar performance of cows of different sizes may be related to the nutritional level of the diet, or the cows may also compensate for the greater maintenance requirement by a greater utilization of the body reserves (MERCADANTE et al, 2003), which might limit their future reproductive performance (CERDÓTES et al, 2004). 1 Difference between the last daily production and the highest production found in the period, in g/days; 2 PEC = (CaWW/CoWC)*100; relation of the amount (kg) of calves weaned for every 100 kg of cows calved; 3 PEW = (CaWW/ CoWW)*100; relation of the amount (kg) of calves weaned for every 100 kg of cows weaned; 4 Total milk production divided by calf weight gain = kg of milk to produce 1 kg of calf; 5 Percentage efficiency of milk production.…”