Selection for components of efficient lean growth rate in pigs 3. Responses to selection with a restricted feeding regime

Abstract

Responses to four generations of divergent selection in pigs for lean growth rate (LGS) with restricted feeding were studied. The selection criterion was designed to obtain equal correlated responses in growth rate and carcass lean content, measured in phenotypic s.d. Animals were to be performance tested in individual pens with a mean starting weight of 30 kg for a period of 84 days. Daily food intake was equal to 0-75 gig of the daily food intake for pigs offered food ad-libitum. In the high, low and control lines, there ivere 1250 Large White-Edinburgh (LW) pigs and 875 British Landrace-Wye (LR) pigs. Each selection line consisted of 10 sires and 20 dams, with a generation interval ofl year. After four generations of selection, cumulative selection differentials were 5-9 and 4-8 phenotypic s.d. for LW and LR populations, with similar responses, 1-8 (s.e. 0-17) phenotypic s.d. Mean weight at the end of test, growth rate and backfat depths at the shoulder, mid back and loin were 89 kg, 712 g/day, 26,13 and 13 mm for LW and for LR pigs were 87 kg, 683 g/day, 28,10 and 10 mm. High line pigs were heavier at the end of test (4-3 (s.e.d. 1-4) kg and 4-0 (s.e.d. 1-6) kg) for LW and LR populations, with corresponding responses in growth rate (54 (s.e.d. 16) g/day and 47 (s.e.d. 18) g/day). Responses in the three backfat depths were -4-1 (s.e.d. 1-2) mm, -2-6 (s.e.d. 0-7) mm and -2-9 (s.e.d. 0-7) mm for LW and -2-2 (s.e.d. 0-05) mm, -2-2 (s.e.d. 0-4) mm and -2-4 (s.e.d. 0-5) mm for LR populations. Responses in weight off test and backfat depths were symmetric about the control lines. Heritabilities for LGS were 0-34 and 0-28 (s.e.d. 0-5) for the LW and LR populations, when estimated by residual maximum likelihood. Common environmental effects for LGS were 0-11 (s.e. 0-03) for LW and 0-17 (s.e. 0-04) for LR. Heritabilities for growth rate and average backfat depth were similar for , as were common environmental effects (0-10 s.e. 0-04). Average phenotypic and genetic correlations between growth rate and backfat, for LW and LR populations, and -0-06 (s.e. 0-16), respectively).Responses to selection and genetic parameter estimates demonstrate that there is substantial genetic variation in growth and fat deposition when pigs are performance tested on restricted feeding.

Genetic parameters and responses of performance and body composition traits in pigs selected for high and low growth rate on a fixed ration over a set time

“…differences in milk production capacity leading to differences between litters in early growth, a component of LDG but not TDG. In other populations fed either on a restricted or semi-restricted scale, the common litter effects were found to range from −3 to 28% for ADG, 32 to 42% for ages to 100 kg, −6 to 26% for UBF and 13 to 19% for TFC [3,4,13,17,22]. Variances due to common litter effects were not significantly greater than zero for any carcass composition traits, in agreement with the estimates reported by Lundeheim et al [17], Merks [22] and Johansson et al [13].…”

“…As market targets for fatness are satisfied, the goal of pig selection for improving efficiency should be directed to reducing the amount of energy used for basal heat production and to increasing the efficiency of energy partitioning between lean and fat tissue growth. Selection for reduced lean food conversion ratio on ad libitum feeding has been shown to place major emphasis on reducing food intake, the numerator of the ratio and only a minor emphasis on increasing growth rate, the denominator of the ratio [4,21]. Restricted feeding appears preferable to ad libitum feeding as a performance testing regimen for improving the ratio since the variation in food intake is suppressed, diverting the selection effort to lean growth.…”

“…Genetic variation in such a characteristic could be the raw material of a genetic selection programme to produce a more profitable pig. Selection for high lean growth rate on a scale feeding [7] has been shown to improve both the rate and efficiency of lean growth, by giving the benefits but not the disadvantages of selection for lean food conversion and lean growth rate on ad libitum feeding [4,21]. However, selection strategies emphasising high leanness was inferred to raise metabolic heat production and the associated rate of glycogen depletion with fasting as measured by muscle acidity [20].…”

Reproductive performance of pigs selected for components of efficient lean growth

“…In the LGA, LGS and LFC selection groups animals were selected on indices combining measurements of performance test traits (Cameron, 1994;Cameron, Curran and Kerr, 1994). In the DFI selection group, the objective was daily food intake.…”

Genotype with feeding regime interaction in pigs divergently selected for components of efficient lean growth rate

“…Details on establishment on the Large White-Edinburgh (LW) and British Landrace-Wye (LR) populations and the four selection groups with divergent selection for lean growth rate on restricted (LGS) or ad libitum (LGA) feeding regimes, lean food conversion ratio (LFC) and daily food intake (DFI), the performance test, selection objectives and criteria are given by Cameron (1994), Cameron and Curran (1994a) and Cameron, Curran and Kerr (1994). Within each selection group, there were high, low and control selection lines.…”