Selection in pigs for increased lean growth rate on a time-based feeding scale

Abstract

Selection was carried out in a line of pigs for increased growth rate of lean tissue. The selection criterion was weight of lean in the ham predicted from live backfat and weight measurements after a 12-week performance test commencing at 25 kg live weight. All pigs were given the same total amount of food over the test period. The scale was set to about proportionately 0-85 of predicted ad libitum intake. Boars selected with an intensity of 1/12 were used for 6 months and sows selected with an intensity of 1/4 were kept for two farrowings. An unselected control line was maintained concurrently.After five generations, performances of selected and control line pigs were compared on ad libitum and scale feeding as they grew to 85 kg. Responses in the selected line on scale feeding were +51 g/day for growth rate (GR), -0-16 for food conversion ratio (FCR), -2-2 mm for backfat (F) and +0-47 kg for ham lean (HL). On ad libitum feeding, responses were much higher in the selected line, giving rise to line x food interactions. Responses were +128 g/day for GR, -0-27 for FCR, -2-3 mm for F, +1-01 kg for HL and +0-15 kg/day for food intake (FI). Estimates of the heritability of HL from variance components were 0-43 (s.e. 0-15) on scale feeding and 0-28 (s.e. 0-19) on ad libitum feeding. The realized heritability of HL on scale feeding was 0-29 (s.e. 0-04) and its co-heritabilities with the other traits on both feeding levels were of similar magnitude to its heritability. Scale feeding exposed genetic variation in the partitioning of food between lean and fat deposition and appeared to be a suitable selection regimen for performance on ad libitum feeding. 149

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

“…Levels of food restriction have been shown by others to influence the sign and magnitude of the genetic correlation between growth rate and backfat thickness [1,12,21]. At both the genetic and phenotypic levels, the correlations between TDG and TFC are close to minus one, reflecting a low variation (CV = 2.1%) between animals in food intake during the test.…”

“…The present selection lines originated from a continuing series of selection experiments in pigs for high efficiency of lean growth over the past 25 years [18,21]. For this study, a new base population was formed by outcrossing sows from the selected lines with superior Large White boars identified in a boar performance testing station.…”

“…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].…”

Estimation of genetic parameters for growth performance and carcass traits in Mukota pigs

“…The genetic correlation between growth rate and leanness has Table 4 Estimates of genetic (above diagonal) and phenotypic correlations (below diagonal) among pre-weaning growth performance, postweaning growth rate and carcass traits from a multi-trait analysis of data from a population of African Mukota pigs reared in a common herd † ADGW ¼ average daily gain from birth to weaning; ADG1 ¼ ADG from weaning to 12 weeks of age; ADG2 ¼ ADG from 12 weeks of age to slaughter; CDM ¼ cold dressed mass, measured after 24 h at 48C; CL ¼ carcass length measured from the anterior edge of the first rib to the pubic bone; K5 ¼ backfat at 50 mm from the mid line along the last rib; K7.5 ¼ backfat thickness at 75 mm from the mid line along the last rib. been shown to be more favourable in young pigs, when feed intake capacity is limited (Campbell et al, 1986;McPhee et al, 1988;Von Felde et al, 1996). The unfavourable positive genetic correlation between ADG2 and backfat is, therefore, an indication that lean deposition in pigs at that age is increasing at a decreasing rate, whereas fat deposition is increasing at an increasing rate or that the pigs are physiologically more mature (Holness, 1991;Kyriazakis and Whittemore, 2006).…”

Effects of genotype, diet and sex on backfat depth in pigs measured physically at different carcass sites and ultrasonically at different liveweights

“…The lean content of pig carcasses is an economically important trait which can be manipulated by nutritional (SCA 1987) and genetic means (McPhee et al 1988). A measurement of subcutaneous fat depth over the M. longissimus dorsi is an accurate and low cost predictor of carcass lean content (Kempster and Evans 1979).…”