Lean Food Conversion Research Articles

Serum urea concentration as a predictor of dietary lysine requirement in selected lines of pigs.

Serum urea concentrations were measured in Large White pigs from lines divergently selected for components of efficient lean growth rate and performance tested over three 14-d test periods starting at 30, 50, and 75 kg. Two methods of performance testing were used. Phase-fed pigs were fed to appetite isoenergetic diets differing in total lysine:energy ratio (0.58, 0.69, 0.81, 0.91, 1.01, 1.12, and 1.23 g/MJ of digestible energy), whereas diet-choice pigs were offered a choice of the 0.69 and 1.12 lysine:energy diets. Between test periods, all animals were fed one diet: 0.91 g of lysine/MJ of digestible energy. The study consisted of 230 boars and gilts with 150 pigs performance tested on phase-feeding and 80 pigs on diet-choice. The line selected for high lean food conversion had lower urea concentrations on each diet than the line selected for high lean growth rate, despite similar predicted lysine balances. Efficiency of lean growth rather than the rate of lean growth may be a better selection strategy in the context of nitrogen excretion. Urea concentrations at the end of each test period were correlated with lysine intake (0.33, 0.48 and 0.65; standard error, 0.08) and predicted lysine balance (0.39,0.44, and 0.64), but were uncorrelated with predicted lysine for protein deposition (0.01, 0.08, and 0.08) and maintenance. Urea concentration at the end of a test period was not a useful predictor of protein deposition, even after accounting for pretest variation in urea concentration and food intake during test. The expected response pattern of serum urea concentration to diets differing in total lysine:energy would be nonlinear, with the point of inflection occurring at the required dietary total lysine:energy for each genotype. However, there was no evidence of such an inflection point such that the prediction of lysine requirement from urea concentration was not possible for the selection lines in the study.

Genetic and nutritional effects on lactational performance of gilts selected for components of efficient lean growth

AbstractLactational performance was measured in Large White gilts from lines that had been divergently selected over seven generations for daily food intake (DFI), lean food conversion ratio (LFC), lean growth rate with ad-libitum (LGA) or restricted (LGS) feeding during performance test. Control line gilts were included in the study. During the lactation period of 21 days, gilts were given to appetite five isoenergetic diets differing in ileal digestible lysine: energy (0·40, 0·58, 0·76, 0·94 and 1·12 g/MJ digestible energy). The study consisted of 223 gilts with a similar number of animals in each selection line.Live-weight loss was greater in the low LFC and LGA lines than in the high lines and food intake was significantly lower in the low LGA line than in the high line. Litter-weight gain of the low LFC and high LGA lines were greater than in the complementary selection lines. Prediction equations for nutrient utilization were used to express the effect of diet and selection line in terms of energy and protein inputs and outputs. Selection on DFI or LGS resulted in gilts that did not mobilize lipid during lactation as sufficient energy for milk and maintenance was provided by dietary intake. In contrast, there was insufficient dietary energy with selection on LFC or on low LGA so lipid mobilization was required to achieve energy balance. The energy required to excrete excess protein and energy from lipid mobilization increased as the dietary lysine energy ratio increased, but there were no other dietary effects on energy and protein utilization. Genotype with nutrition interactions were detected for energy intake and lipid mobilization, which were due to the lines selected for low DFI and LGA. The general absence of genotype with nutrition interactions for lactational performance in gilts selected for components of efficient lean growth and the lack of significant dietary effects on energy utilization indicated that the consequences of changing nutritional inputs will be broadly similar for genotypes within the set of genotypes studied. Selection strategies which result in reduced food intake during lactation should be avoided if lipid mobilization is then required to attain energy balance and there are resultant negative effects on subsequent reproductive performance.

Peri-partum posture and behaviour of gilts and the location of their piglets in lines selected for components of efficient lean growth

Peri-partum posture and behaviour of gilts from lines selected for different components of efficient lean growth were studied to determine if behavioural changes may have been associated with the observed responses in reproductive performance. The proportions of time that gilts expressed defined posture and behaviour traits and the locations of their piglets were determined from video recordings of observations made at 5 min intervals in the period extending from 2 h pre-farrowing to 2 h post-farrowing. The 137 gilts studied were from four pairs of Large White lines which had been divergently (high and low) selected for either daily food intake (DFI), lean food conversion efficiency (LFC), lean growth rate on ad libitum feeding (LGA) or lean growth rate on a restricted feeding scale (LGS). Almost all the significant ( P<05) changes occurred in the LGS pair of lines. In the pre-farrowing period, relative to the low LGS gilts, high LGS gilts spent a higher proportion of their time lying on their sides (0.92 versus 0.69), and less time in the upright postures of standing, sitting or lying on their bellies (0.08 versus 0.33) and engaging in nesting behaviour (0.02 versus 0.10). During farrowing, high LGS gilts again lay on their sides more often than low LGS gilts (0.96 versus 0.80) and were upright less often (0.04 versus 0.20). High LGS gilts changed posture less often than low LGS gilts (0.05 versus 0.31) but were more often alert (0.79 versus 0.61). During farrowing, high LGS piglets were seen less often at their mother’s head, back and vulva or at the creep than low LGS piglets (0.06 versus 0.15). Post-farrowing, there were no significant differences between the lines, almost all gilts lying on their sides with their piglets at the udder. Divergent selection for components of efficient lean growth rate on ad libitum feeding was not associated with consistent responses in gilt posture and behaviour or in piglet location. Selection for high lean growth on restricted feeding had effects on gilt posture and behaviour which may have been beneficial to her welfare and that of her piglets.

Sensitivity of pig genotypes to short-term manipulation of plasma fatty acids by feeding linseed

The sensitivity of pigs selected for high daily food intake (DFI), low lean food conversion (LFC) and high lean growth rate (LGS) to dietary change of plasma fatty acids was assessed. The difference between the two diets was effectively a substitution of palmitic (C16:0), oleic (C18:1 n-9) and linoleic (C18:2 n-6) with linolenic (C18:3 n-3) fatty acids. Fatty acid compositions of plasma free fatty acids, neutral lipids and phospholipids were measured in 90 kg animals fed a base or high linolenic (C18:3 n-3) fatty acid diet, based on whole linseed, for four days. There were 24 animals from each selection line and 24 animals from an unselected control line, with boars and gilts represented equally in each line. Half of the selection line animals were fed the base diet and half were fed the high C18:3 diet, but all control animals were fed the base diet. Prior to slaughter, animals were fasted for 18 h. The fatty acids primarily affected by dietary change were C18:3 n-3 and its products, C20:5 n-3 (EPA) and C22:6 n-3 (DHA). The sensitivity of a selection line to dietary change was parameterised by the relative shift in fatty acid composition through changing from the base diet to the high C18:3 diet. In neutral lipids, the sensitivities of C18:3 n-3 in the DFI and LFC lines were similar but greater than in the LGS line (3.0 v. 1.8, S.E.D. 0.15), while, for phospholipid and free fatty acids, the sensitivity of the DFI line was greater than in the LFC and LGS lines (2.3 v. 1.8 and 2.0 v. 1.4, respectively). For C20:5 n-3 and C22:6 n-3, the DFI and LFC lines were more sensitive to dietary change than the LGS line (total lipid : 2.3 v. 1.9 and 1.5 v. 1.2). In general, the DFI line was most sensitive to dietary change and the LGS line was the least sensitive. The difference in sensitivities of the lipid classes to the high C18:3 diet between the selection lines could result from differences in body fat content and may explain the general lack of genotype with nutrition interactions in post-1990 genotypes in comparison with fatter circa-1970 genotypes.

Genotype with nutrition interaction on fatty acid composition of intramuscular fat and the relationship with flavour of pig meat

The effects of genotype, diet and the genotype with diet interaction on fatty acid composition of neutral lipid and phospholipid of intramuscular fat in pigs were examined. Pigs from four selection lines and a control line were fed isoenergetic diets, which differed in ileal digestible lysine:digestible energy (A: 0.40, C: 0.76 and E: 1.12 g lysine/MJ DE). The selected lines resulted from seven generations of selection for high daily food intake (DFI), lean food conversion ratio (LFC) and lean growth rate on ad-libitum (LGA) or restricted feeding regimes in a Large White population. During performance test, from 30 to 90 kg, pigs were fed on either ad-libitum or restricted (0.75 g/g ad-libitum daily food intake) feeding regimes. A trained sensory panel assessed intensities of pork flavour and abnormal flavour and the hedonic characteristics of flavour liking and overall acceptability. The proportion of neutral lipid in the LGA line was lower (0.64 v 0.75, s.e.d. 0.03) while the polyunsaturated:saturated (P:S) ratio of the LFC line (0.53 v 0.41, s.e.d. 0.05) was higher than the control line and other selection lines. The DFI line had a higher phospholipid n-6:n-3 ratio than other selection lines (14 v 11, s.e.d. 1.0). Diets C and E resulted in lower neutral lipid:phospholipid ratio (0.7 v 0.8, s.e.d. 0.01), n-6:n-3 ratios for both neutral lipid (5 v 13, s.e.d. 0.8) and phospholipids (7 v 20, s.e.d. 0.6) and a higher P:S ratio (0.5 v 0.3, s.e.d. 0.03) for neutral lipid than diet A. Neutral lipid fatty acids C18:2 n-6, C18:3 n-3, C20:3 n-6, C20:4 n-6, C20:5 n-3, C22:5 n-3 and C22:6 n-3 were negatively correlated with pork flavour (−0.30, s.e.d. 0.10), flavour liking (−0.33) and overall acceptability (−0.30). In contrast, the fatty acids C16:1, C18:1 ω9 and C18:1 ω11 were positively correlated with pork flavour (0.36), flavour liking (0.39) and overall acceptability (0.40). However, correlations for fatty acids in the phospholipid class were positive for C18:2 n-6, C20:4 n-6 and C22:4 n-6 with pork flavour (0.33), flavour liking (0.23) and overall acceptability (0.23). The proportion of neutral lipid had non-significant correlations with flavour traits; pork flavour (0.01), abnormal flavour (0.08), flavour liking (−0.03) and overall acceptability (0.03). The selection lines responded in a similar manner to the different diets, such that there was little evidence for genotype with nutrition interactions for fatty acid concentrations of neutral lipids and phospholipids. Selection for high lean growth will reduce intramuscular fat, but the increased relative amount of phospholipid and concentration of polyunsaturated fatty acids are unlikely to reduce eating quality. Nutritional effects on intramuscular fat characteristics were greater than genetic effects, such that nutritional approaches to feeding pigs will provide effective methods of reducing the n-6:n-3 fatty acid ratio of human dietary fat from pigmeat and improving human health.

Boar taint in pigs selected for components of efficient lean growth rate

Genetic and nutritional effects on the boar taint traits of androstenone, skatole and indole and the eating quality traits associated with boar taint were examined by testing animals from four selection lines and a control line on isoenergetic diets, which differed in ileal digestible lysine: digestible energy (0.40, 0.76 and 1.12 g lysine/MJ DE). The selected lines resulted from seven generations of selection for high daily food intake, lean food conversion ratio (LFC) and lean growth rate on ad libitum (LGA) or restricted (LGS) feeding regimes in a Large White population. During performance test, from 30 to 90 kg, boars were fed on either ad libitum or restricted (0.75 g/g ad libitum daily food intake) feeding regimes. A sensory panel assessed heated fat samples for androstenone odour, skatole odour and abnormal odour. There were no significant differences between the selection and control lines or diets for log transformed fat content of androstenone, skatole, indole. The significant diet with feeding regime interaction for log transformed fat content of skatole and indole were essentially due to significantly higher log transformed fat contents with ad libitum feeding of the high lysine diet compared to restricted feeding (skatole: −1.94 vs −3.06, s.e.d. 0.43; indole: −3.44 vs −4.22, s.e.d. 0.28), as differences between feeding regimes on diets A and C were not significantly different from zero. There were no significant differences between selection and control lines for sensory panel score for abnormal odour or androstenone odour, but the LFC and LGA selection lines had a significantly higher skatole odour score than the LGS selection line. Neither diet nor feeding regime had any significant effect on sensory panel assessment of odour. Log transformed fat content of androstenone and skatole were significantly correlated with sensory panel score for skatole odour (0.37 and 0.46, s.e. 0.12), but not with sensory panel score for androstenone odour (0.06 and 0.09), such that they would not be useful predictors of androstenone odour.

Genetic and nutritional effects on age at first oestrus of gilts selected for components of efficient lean growth rate

Genetic and nutritional effects on age at first oestrus of gilts selected for components of efficient lean growth rate

Genotype with nutrition interactions for carcass composition and meat quality in pig genotypes selected for components of efficient lean growth rate

AbstractGenotype with nutrition interactions in carcass composition and meat quality traits were examined by testing pigs from four selection lines and a control line on isoenergetic diets, which differed in lysine: energy content. The selected lines resulted from seven generations of selection for high daily food intake, lean food conversion ratio (LFC) and lean growth rate onad-libitumor restricted (LGS) feeding regimes in a Large White population. There were 128 pigs in the study, with 24 pigs per selection line and 32 pigs from a control line. During performance test, 30 to 90 kg, pigs were offered one of three isoenergetic diets, 14·0 MJ digestible energy (DE) per kg dry matter, which differed in ileal digestible lysine: digestible energy (A: 0·40 , C: 0·76 and E: 1·12 g lysine per MJ DE) onad-libitumor restricted (0.75 g/gad-libitumdaily food intake) feeding regimes.For the majority of performance test, carcass composition and meat quality traits there was no evidence of a genotype with diet or genotype with feeding regime interaction. The selection line with feeding regime interactions for average daily gain, daily food intake and rates of lean and subcutaneous fat deposition were primarily due to no feeding regime effect for the LFC selection line. Selection for high LFC had reducedad-libitumdaily food intake to such an extent that it was not significantly different from daily food intake on a restricted feeding regime, unlike other selection lines in the study. A selection line with feeding regime interaction was detected for muscle рH24hand muscle reflectance, which resulted from the LGS selection line. LGS pigs offered food ad libitum had higher muscle рH24hand lower muscle reflectance than LGS pigs given food at a restricted level, while there was no effect of feeding regime for the other selection lines.The general absence of genotype with nutrition interactions for traits measured in the study indicated that the ranking of genotypes for performance test traits, carcass composition and meat quality traits will not be dependent on diet or feeding regime. Genotype specific nutritional inputs will also not be required for identification of pigs of high genetic merit, within a genotype. However, diet and feeding regime had significant effects on carcass composition and meat quality traits, such that the estimated mean value of a genotype will be dependent on the diet or feeding regime used to evaluate the genotype.

Meat quality of Large White pig genotypes selected for components of efficient lean growth rate

AbstractResponses in carcass composition and meat quality after seven generations of selection for components of lean growth rate were examined in a population of Large White pigs. There were four selection groups in the study, with divergent selection for lean growth rate on ad libitum (LGA) or restricted (LGS) feeding regimes, lean food conversion ratio (LFC) and daily food intake (DFI). In generations six and seven, two offspring from each of 10 sires, within each selection line, were to be allocated for half-carcass dissection and measurement of meat quality. There were 320 animals in the study, with 40 animals from each of the high and low selection lines and, within each selection line, two offspring per sire.Responses in carcass composition were similar in the three selection groups given food ad libitum, but rates of lean and fat growth rate differed between selection lines. Intramuscular fat content was reduced with selection for high LGA and high LFC but was increased with selection for low DFI (-1·7 and -3·2 v. 2·7 (s.e.d. 0·7) mg/g), which was unexpected given the higher carcass fat content of the low DFI line, relative to the high line (249 v. 190 (s.e.d. 7) g/kg). Muscle colour was darker, as measured by trained sensory panel assessment, in selection lines which reduced the rate of fat deposition to achieve a leaner carcass (high LFC and low DFI) but there was no response in muscle colour with selection for LGA (0·4 and 0·3 v. 0·0 (s.e.d. 0·1)). Responses in muscle shear force (5·3 v. 4·4 (s.e.d. 0·4) kg) and flavour liking (4·0 v. 4·3 (s.e.d. 0·12)) were limited to the LGA and LFC selection groups, respectively. There were no significant responses in muscle moisture content, muscle pH or myofibrillar fragmentation index, nor were there any responses in meat quality with selection on LGS. Therefore, decreasing the rate of fat deposition was associated with darker meat and increasing the rate of lean growth was associated with higher shear force. There were selection strategy specific responses in the fatty acid composition of intramuscular fat, which may have contributed to the responses in eating quality.In general, responses in meat quality were small, such that incorporation of meat quality traits in selection objectives, which are primarily focused on increasing the efficiency of lean meat production, may not be necessary. However, it would be pertinent to evaluate periodically genotypes of breeding companies for muscle quality traits.

Relationships between muscle fibre traits with meat and eating quality in pigs

Knowledge of the genetic and phenotypic relationships for muscle fibre characteristics with meat and eating quality in pigs is required by the pig breeding industry for two reasons. Muscle fibre traits, determined from muscle biopsy, could be used as genetic predictors of meat and eating quality traits and, secondly, if responses in meat and eating quality traits are partially due to changes in muscle fibre traits, then selection criteria can be designed to compensate for such responses. The current study estimated the genetic and phenotypic relationships for muscle fibre traits with meat and eating quality traits.The study consisted of 160 Large White pigs from lines divergently selected for lean growth rate on ad-libitum or restricted feeding regimes, lean food conversion ratio and daily food intake for seven generations in the Edinburgh lean growth selection experiment. Within each selection line, there were 10 pairs of full-sibs. Boars and gilts were tested from 30 kg, individually penned and fed a diet consisting of 224 g CP/kg DM and 15.9 MJ DE/kg DM.

Relationships between muscle fibre traits with meat and eating quality in pigs

Knowledge of the genetic and phenotypic relationships for muscle fibre characteristics with meat and eating quality in pigs is required by the pig breeding industry for two reasons. Muscle fibre traits, determined from muscle biopsy, could be used as genetic predictors of meat and eating quality traits and, secondly, if responses in meat and eating quality traits are partially due to changes in muscle fibre traits, then selection criteria can be designed to compensate for such responses. The current study estimated the genetic and phenotypic relationships for muscle fibre traits with meat and eating quality traits.The study consisted of 160 Large White pigs from lines divergently selected for lean growth rate on ad-libitum or restricted feeding regimes, lean food conversion ratio and daily food intake for seven generations in the Edinburgh lean growth selection experiment. Within each selection line, there were 10 pairs of full-sibs. Boars and gilts were tested from 30 kg, individually penned and fed a diet consisting of 224 g CP/kg DM and 15.9 MJ DE/kg DM.

Responses in gilt post-farrowing traits and pre-weaning piglet growth to divergent selection for components of efficient lean growth rate

AbstractResponses in gilt live weight, backfat depth and food intake during lactation and in pre-weaning piglet growth rate were examined after seven generations of divergent selection for daily food intake (DFI), lean food conversion (LFC) or lean growth rate (LGA) on ad-libitum feeding or lean growth on restricted feeding (LGS). There were 252 Large White gilts in the study. Selection for low DFI resulted in gilts with less backfat (25·7 v. 30·7 (s.e.d. 2·21) mm) at farrowing and a substantially lowerfood intake (129 v. 146 (s.e.d. 5) kg) during lactation, but similar reductions in live weight (42 (s.e.d. 6) kg) and backfat depth (8·4 (s.e.d. 1·7) mm) than with selection for high DFI. Therefore, the lower piglet growth (167 v. 295 (s.e.d. 11) g/day) with selection for low DFI compared with selection for high DFI was primarily due to lower food intake of the gilts, as energy for milk production from food was reduced. In contrast, selection for high LFC resulted in relatively smaller changes in live weight (37 v. 48 (s.e.d. 5) kg) and backfat depth (7·6 v. 8·9 (s.e.d. 1·3) mm) than selection for low LFC, which combined with a lower food intake (132 v. 148 (s.e.d. 4) kg) during lactation, resulted in lower piglet growth (181 v. 200 (s.e.d. 11) g/day). The higher food intake of high LGA gilts (137 v. 121 (s.e.d. 4) kg) compensated for the relatively lower reductions in live weight (41 v. 46 (s.e.d. 5) kg) and backfat depth (5·5 v. 6·7 (s.e.d. 1·3) mm) during lactation compared with the low LGA line, such that piglet growth was similar (195 v. 289 (s.e.d. 11) g/day) in the two selection lines. In the high and low LGS selection lines, piglet growth was similar (195 v. 186 (s.e.d. 11) g/day) as was gilt food intake (125 v. 227 (s.e.d. 5) kg) and the changes in live weight (39 v. 41 (s.e.d. 6) kg) and backfat depth (8·1 v. 7·7 (s.e.d. 2·2) mm) during lactation. An examination of the daily energy used in litter gain and the energy available from gilt food intake and mobilization of body lipid indicated that one equation to predict the amount of body lipid mobilized during lactation was not appropriate for different genotypes. Responses in gilt food intake and the changes in live weight and backfat during lactation were selection strategy dependent. However, in general, the selection strategies which reduced gilt voluntary food intake during lactation or resulted in lower live weight and backfat depth at farrowing were detrimental to piglet growth rate.

Responses in gilt traits measured during performance test, at mating and at farrowing with selection for components of efficient lean growth rate

AbstractThe responses in traits measured at the start of the mating period and at farrowing were examined after seven generations of divergent selection for daily food intake (DFI), lean food conversion (LFC), lean growth rate (LGA) on ad-\ibitum feeding and lean growth on scale feeding (LGS). Weight and backfat depth at mating were measured on 330 gilts and 74 boars, which were selected on the basis of performance test traits. Farrowing information was available on 259 gilts. At the start of the mating period, gilts selected for high DFI, LGA or LGS had similar live weights (135, 137 and 137 (s.e.d. 4·5) kg) but different backfat depths (20·3, 14·0 and 11·3 (s.e.d. 1·3) mm) while the corresponding low lines had different live weights (129, 117 and 124 kg), but similar backfat depths (17·5, 17·8 and 17·8 mm). Gilts selected for high LFC had lower mean live weight and backfat depth (114 kg and 10·7 mm) than gilts in the other selection lines. Conception rates of gilts selected for low DFI or high LGS were similar (0·62 and 0·64, s.e.d. 0·12) and lower than for the alternative selection strategies (0-78), but the low DFI gilts were significantly older at farrowing than gilts selected for high LGS (424 v. 408 (s.e.d. 5·5) days). Responses in live weight, backfat depth, age at mating and particular reproduction traits were selection strategy dependent, such that identification of relationships between growth and reproduction traits will require measurement of additional growth traits at an earlier age than in the current study

Responses in gilt post-farrowing traits and pre-weaning piglet growth to divergent selection for components of efficient lean growth rate

Responses in sow traits at farrowing and during lactation and in pre-weaning piglet growth rate were determined in a population of Large White pigs, after seven generations of divergent selection for components of efficient lean growth rate. Information on the factors influencing preweaning piglet growth rate is required for a comprehensive evaluation of alternative selection strategies.There were four selection groups: daily food intake (DFI), lean food conversion (LFC), lean growth rate (LGA) on ad-libitum feeding and lean growth rate on scale feeding (LGS). There were 242 gilts in the study, with 20 gilts in the high, low and control lines of each selection group. Pigs in the ad-libitum selection groups were performance tested over a fixed weight range of 30 to 85 kg. Pigs fed on scale feeding were performance tested for a fixed time period of 84 days from 30 kg with food intake equal to 0.75 g/g of daily ad-libitum food intake. Matings were unsupervised and took place in outside paddocks.

Responses in gilt post-farrowing traits and pre-weaning piglet growth to divergent selection for components of efficient lean growth rate

Responses in sow traits at farrowing and during lactation and in pre-weaning piglet growth rate were determined in a population of Large White pigs, after seven generations of divergent selection for components of efficient lean growth rate. Information on the factors influencing preweaning piglet growth rate is required for a comprehensive evaluation of alternative selection strategies.There were four selection groups: daily food intake (DFI), lean food conversion (LFC), lean growth rate (LGA) on ad-libitum feeding and lean growth rate on scale feeding (LGS). There were 242 gilts in the study, with 20 gilts in the high, low and control lines of each selection group. Pigs in the ad-libitum selection groups were performance tested over a fixed weight range of 30 to 85 kg. Pigs fed on scale feeding were performance tested for a fixed time period of 84 days from 30 kg with food intake equal to 0.75 g/g of daily ad-libitum food intake. Matings were unsupervised and took place in outside paddocks.

Variation in energy requirements to maintain liveweight in pigs divergently selected for efficiency of lean growth

The energy requirement for maintenance in pigs has been suggested to be a function of liveweight (W), using equations such as 0.46 MJ digestible energy (DE)/g W0.75 (ARC, 1981). For a 60 kg pig, the predicted energy required for maintenance can proportionately account for 0.30 of the daily energy intake. Therefore, substantial reductions in pig production costs could be achieved, if the energy required for maintenance was reduced. The present study estimated the energy required to maintain liveweight, rather than the energy required for maintenance, as the latter assumes no change in protein or lipid content of the animal. Genotypes from the Edinburgh lean growth selection experiment provided the experimental resource to determine if selection for lean food conversion ratio over seven generations had changed the DE required to maintain liveweight.

Variation in energy requirements to maintain liveweight in pigs divergently selected for efficiency of lean growth

The energy requirement for maintenance in pigs has been suggested to be a function of liveweight (W), using equations such as 0.46 MJ digestible energy (DE)/g W0.75 (ARC, 1981). For a 60 kg pig, the predicted energy required for maintenance can proportionately account for 0.30 of the daily energy intake. Therefore, substantial reductions in pig production costs could be achieved, if the energy required for maintenance was reduced. The present study estimated the energy required to maintain liveweight, rather than the energy required for maintenance, as the latter assumes no change in protein or lipid content of the animal. Genotypes from the Edinburgh lean growth selection experiment provided the experimental resource to determine if selection for lean food conversion ratio over seven generations had changed the DE required to maintain liveweight.

Responses in carcass composition to divergent selection for components of efficient lean growth rate in pigs

AbstractCarcass composition was measured after six generations of divergent selection for lean growth rate on ad-libitum and restricted feeding, lean food conversion and daily food intake in populations of Large White (LW) and Landrace (LR) pigs. There were 161 half-carcass dissections in LW pigs and for LR pigs, a double sampling procedure combined information from 53 half-carcass and 53 hand joint dissections. The performance test started at 30 kg and finished at 85 kg with ad-libitum feeding and after 84 days with restricted feeding, and pigs were slaughtered at the end of the test.In the LR population, selection for lean growth on restricted feeding increased carcass lean content (605 v. 557 (s.e.d. 19) g/kg), but there were no significant responses in carcass lean content with the selection strategies on adlibitum feeding. Selection for lean food conversion and high lean growth on restricted feeding reduced carcass fat content (201 v. 241 (s.e.d. 14) and 150 v. 218 (s.e.d. 18) g/kg), but selection for high lean growth rate with adlibitum increased carcass fat content (212 v. 185 (s.e.d. 11) g/kg). Responses in carcass composition were not significant with selection on daily food intake.In the LW population, selection for high lean food conversion or low daily food intake increased carcass lean content (539 v. 494 and 543 v. 477 (s.e.d. 11) g/kg) to a greater extent than selection on lean growth rate (509 v. 475 g/kg). Responses in carcass fat content were equal and opposite to those in carcass lean content. Selection on lean growth rate with ad-libitum feeding increased lean tissue growth rate (LTGR) (491 v. 422 (s.e.d. 23) g/day), but there was no change in fat tissue growth rate (FTGR) (206 v. 217 (s.e.d. 15) g/day). In contrast, FTGR was reduced with selection on lean food conversion (169 v. 225 g/day), but LTGR was not significantly increased (520 v. 482 g/day). Selection for lean growth rate with restricted feeding combined the desirable strategies of lean growth rate on adlibitum feeding and lean food conversion, as LTGR was increased (416 v. 359 (s.e.d. 12) g/day) and FTGR decreased (126 v. 156 (s.e.d. 7) g/day). The preferred selection strategy may be lean growth rate on restricted feeding, which simultaneously emphasizes rate and efficiency of lean growth.For ad-libitum fed LW pigs, coheritabilities for growth rate, daily food intake and backfat depth with carcass lean content were negative (-0·12, -0·22 and -0·50 (s.e. 0·05), but positive with carcass subcutaneous fat content (0·22, 0·24 and 0·50), when estimated from six generations of performance test data and carcass dissection data in generations 2, 4 and 6.

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

AbstractThe genotype with feeding regime interaction was examined by testing pigs from four selection groups on both ad libitum and restricted feeding regimes. Within each selection group, there were high, low and control lines, which had been selected for lean food conversion ratio (LFC), daily food intake (DFI) or lean growth rate on ad libitum (LGA) or on restricted (LGS) feeding, in Large White-Edinburgh (LW) and Landrace-Wye (LR) populations. There were 1187 LW pigs and 768 LR pigs in the study, with 344 LW and 133 LR pigs tested on the alternative feeding regime.In the LW population, pigs in the high LGS line grew significantly faster than the high LGA and LFC lines with ad libitum feeding (919 v. 847 and 786 (s.e.d. 31) g/day), but had similar food conversion ratios and backfat depths. The high LGS and high DFI lines were similar for growth rate, daily food intake and food conversion ratio, but backfat depth was significantly lower in the high LGS line than in the high DFI line (12·0 v. 25·9 (s.e.d. 0·7) mm). On restricting feeding, the rankings of the selection lines for growth rate, food conversion ratio and mid-back fat depth were broadly similar to those with ad libitum feeding, except for the high LFC line. In the LR population, the high LGS, LGA and LFC lines did not differ significantly in growth rate, daily food intake, food conversion ratio and backfat depth within either the ad libitum or restricted feeding regimes. Growth rate of the high LGS line was similar to the high DFI line on ad libitum feeding (828 v. 836 (s.e.d. 40) g/day), but significantly higher on restricted feeding (704 v. 636 (s.e.d. 23) g/day). On both feeding regimes, food conversion ratio and backfat depth were significantly lower in the high LGS line compared with the high DFI line.In the LW population, the genetic correlation between feeding regimes for growth rate was significantly less than one (0·4 (s.e. 0·20)), but was not significantly different from unity (0·8 (s.e. 0·14)) for backfat depths. Based on the performance test results, selection for lean growth with testing on a restricted feeding regime may be preferable to testing animals on an ad libitum feeding regime.

Reproductive performance of pigs selected for components of efficient lean growth

AbstractCorrelated responses in reproductive performance to five generations of divergent selection for daily food intake (DFI), lean food conversion (LFC), lean growth rate on ad–libitum feeding (LGA), and lean growth rate on scale feeding (LGS) were studied. Litter traits were measured on 1220 Large White gilts. Mean litter weights at birth and weaning were 12·9 kg and 63·5 kg, with average litter sizes of 10·3 and 7·9. Responses to selection in the high and low lines for litter size in the DFI and LFC selection groups were 1·9 and –1·5 (s.e.d. VI) at birth and 0·9 and –1·8 (s.e.d. 1·2) at weaning. Responses in litter birth weights were respectively positive and negative for DFI and LFC (3·0 and –2·8 (s.e.d. 1·4) kg) and the response in LGS (3 kg) was greater than in LGA (–0·1 kg). Selection line differences in litter weaning weight followed a similar pattern to birth weight for DFI and LFC (17·5 and –17·3 (s.e.d. 10·1) kg). Responses in litter weights were a result of selection line differences in both litter sizes and piglet weights. The relationships between litter size, litter weights and piglet weights at birth and weaning were essentially linear. An extra piglet at birth and weaning corresponded to an increase of 1·0 (s.e. 0·02) kg and 6·9 (s.e. 0·1) kg in litter weights. Piglet birth and weaning weights were decreased by 0·03 (s.e. 0·003) kg and 0·19 (s.e. 0·02) kg. A uterine constraint on piglet growth was implied, but there was no evidence for a limit to uterine capacity. Heritabilities for litter size, weight and piglet weight at birth of 0·06, 0·11 (s.e. 0·04) and 0·16 (s.e. 0·02) respectively were similar to those at weaning. Common environmental effects on piglet weights at birth and weaning were substantially higher than the heritabilities (0·38 and 0·45, s.e. 0·01). The study indicated that selection for lean growth on either an ad–libitum or restricted feeding regime did not significantly affect reproductive performance, but the high lean food conversion ratio and low daily food intake selection lines had impaired reproductive performance.