Relationship between energy intake and growth performance and body composition in pigs selected for low backfat thickness

Genetic selection of pigs over recent decades has sought to reduce carcass fat content to meet consumer demands for lean meat in many countries (e.g.: Australia). Due to the impacts of genetic changes, it is unknown whether the carcass fat measures are still responsive to energy intake. Thus, the present experiment aimed to quantify the relationship between tissue composition and dietary energy intake in finisher pigs selected for low carcass backfat. Intact male and female pigs (n=56 for each sex; PrimegroGenetics, Corowa, NSW, Australia) were fed seven different amounts of an amino acid adequate wheat-based diet containing 14.3 MJ digestible energy (DE)/kg to provide the following daily DE intakes- 25.8, 29.0, 32.6, 35.3, 38.5, 41.5 and 44.2 (ad libitum) MJ DE/d for males, and 25.8, 28.9, 32.0, 35.6, 38.3, 40.9 and 44.5 (ad libitum) MJ DE/d for females between 60 kg and 108 kg live weight. Body composition of anaesthetised pigs was measured using the Dual Energy X-ray Absorptiometry (DXA) method when individual pigs reached 108 kg, and protein, fat and ash deposition rates were calculated. Pigs were slaughtered on the 2nd day post-DXA scan for carcass backfat measurement. The results showed that the carcass backfat thickness (standardized at 83.7 kg carcass) increased by 0.125 mm for every MJ increase in daily DE intake in male pigs (P = 0.004; R2 = 0.130), but carcass backfat of female pigs (standardized at 85.1 kg carcass) was not responsive to daily DE intake. Whole-body fat composition and fat deposition rate increased linearly (both P < 0.01) in male pigs but quadratically (both P < 0.01) in female pigs in response to DE intake. Every MJ increase of daily DE intake increased the rate of daily protein deposition by 3.8 g in intact male pigs (P < 0.001; R2 = 0.781) and by 2.5 g in female pigs (P < 0.001; R2 = 0.643). In conclusion, the selection for low backfat thickness over the last two decades has altered the response of fat deposition and backfat thickness to energy intake, particularly in female pigs. Despite this change, the linear relationship between DE intake and protein deposition rate was maintained in these modern genetics.

Improving growth performance of finisher pigs with high fat diets

A total of 1296 pigs (Large White × Landrace) were selected at 16 weeks of age and used to investigate the effects of supplemental dietary fat concentration on finisher growth performance. Pigs were selected at an average weight of 64.0 kg and allocated to a 2 × 6 factorial experiment with the respective factors being sex (entire male and female) and supplemental dietary fat concentration (1, 2, 3, 4, 5 and 6% added tallow). All pigs were offered the respective diets ad libitum from 16 weeks of age through to slaughter at 21 weeks of age. Over the entire 5-week period, feed : gain ratio improved linearly with increasing supplemental fat concentration (P < 0.001), reducing from 2.60 to 2.44 with an increase in dietary fat concentration from 1 to 6%. Improvements in daily gain were more pronounced during the initial 14-day feeding period, increasing linearly (P = 0.002) from 844 g/day (1% fat) to 942 g/day (6% fat). Carcass weight also improved linearly (P = 0.009), increasing from 74.1 kg (1% fat) to 75.8 kg (6% fat). A greater response was observed in the males, with an increase in supplemental fat concentration from 1 to 6% improving daily gain by 7%, reducing the feed: gain ratio from 2.55 to 2.31 and improving profit per pig by AU$4.17. The effects of increasing dietary fat concentration were more moderate in females, with potential profit increases of AU$1.47. These results suggest that adding up to 6% supplemental fat to finisher diets improves profit under Australian conditions, with the benefits greater in male than female pigs. The economic impact of such a feeding strategy will, however, depend on the pig’s genetic propensity for fat deposition and the pricing system in which the pigs are sold.

Influence of energy intake on protein and lipid deposition in Creole and Large White growing pigs in a humid tropical climate

Twenty-four castrated males were used to study the effect of breed (Large Whitev. Creole (LWv. CR)) and feeding level (0·70, 0·80, 0·90, and 1·00 ad libitum) on growth performance and protein deposition (PD) and lipid deposition (LD) between 30 and 60 kg in growing pigs under tropical climatic conditions; the CR pigs are raised in the Caribbean area and can be qualified as fat and slow growing pigs. Daily protein and amino acids supplies were calculated to be non-limiting for protein gain. Total PD and LD were measured according to the comparative slaughter technique. Digestibility coefficients of energy and nutrients were estimated over a 10-day period at 45 kg live weight. Neither the breed nor the feeding level influenced the apparent digestibility coefficients of dietary nutrients; only energy digestibility was increased at reduced feeding levels (P<0·05). Average daily gain increased linearly with the increase of metabolizable energy (ME) intake and the slope of the relationship was lower in CR than in LW pigs (30·4v. 36·6 g per additional MJ ME). The food conversion ratio was not affected by feeding level but it was significantly higher in CR than in LW pigs (2·88v. 2·36 kg /kg;P<0·001). Daily PD increased with ME intake according to a linear relationship in both breeds and the slope was significantly affected by breed (3·1v. 4·2 g/MJ ME in CR and LW pigs, respectively;P<0·001). In contrast, the increase of LD and total energy retained with ME were higher in CR than in LW pigs (8·4v. 6·4 g/MJ and 0·40v. 0·36 MJ/ MJ ME, respectively;P<0·001).

Longitudinal DXA measurements demonstrate lifetime differences in lean and fat tissue deposition between boars and barrows under individual and group-penned systems

Thirty-two Large White × Landrace male pigs were used to determine the relationships between the rates of tissue deposition and age, in boars and barrows under 2 housing systems. A 2 × 2 factorial design was used, with the respective treatments being sex (boar or barrow) and housing condition (individually penned system or group-penned system). Surgical castration was performed at 7 days of age. Individually housed pigs were used to provide an estimate of potential growth and were weaned at 10 days into individual cages and provided with supplemental fermented skim milk for 2 weeks. Group-housed pigs were weaned at 24 days of age and reared in group pens of boars and castrates typical for commercial production. Conventional weaner, grower, and finisher diets were provided ad libitum to all pigs from weaning onwards. A Hologic QDR4500A dual-energy X-ray absorptiometer (DXA) was used to determine lean, fat, and bone composition at 4-weekly intervals from 10 until 150 days of age. Over the 20 weeks of the study, boars deposited less fat than barrows (136 v. 179 g/day, s.e.d. = 6.49, P < 0.001). Over the same time frame, boars deposited more lean tissue than barrows when individually penned (490 v. 444 g/day, s.e.d. = 14.4, P < 0.05) but there was no difference in group-penned pigs (464 v. 443 g/day, s.e.d. = 14.4, P > 0.1). This was more pronounced in the final 4 weeks of growth when individually penned boars deposited 200 g/day more lean than barrows (P < 0.001), with no increase in group-penned animals. However, during this growth phase, group penning further increased the fat deposition margin between boars and barrows where boars deposited 90 g/day less fat when individually penned (P < 0.001), but 140 g/day less fat (P < 0.001) when group penned. The results show that the advantages of boars in terms of growth and lean tissue composition are substantially reduced in group-penned situations. However, because of fat deposition, boars retain some advantage over barrows in group-penned systems at liveweights over about 50 kg. These data may aid in the accurate prediction of the nutrient requirements and optimum slaughter weight for barrows.