This would result in the most efficient feeding programs, producing pork of high quality at the lowest possible price. This experiment was carried out to define the lean tissue and lipid growth curves of a common commercial genotype.

Peak protein deposition was found in barrows to be 150 g/d and occurred when the pig was between 43 and 52 kg bodyweight. In gilts, maximum protein deposition of 133 g/d occurred between 68 and 74 kg bodyweight. Barrows deposited protein at a greater rate than gilts until 87 kg bodyweight.

Observed differences in protein and lipid deposition between genders explain differences in amino acid and energy requirements. These findings reinforce the need for split sex and multiple phase feeding programs, to maximize production efficiency and carcass quality. Most critically, these results provide information on a subject of limited information – what is the rate of protein deposition of commercial pigs.

INTRODUCTION

Pigs that have been intensively selected for body weight gain or lean tissue deposition have a higher maximum protein retention than pigs of unimproved strains. Defining the amino acid requirements for these improved strains requires accurate estimates of whole body protein deposition from birth to market weight. The rate of maximal protein deposition determines the pig's nutrient requirements for growth and its likely response to nutrition or management changes.

The objectives of this study were to characterize the upper limit to protein deposition, lipid growth curves and feed intake and feed efficiency curves for barrows and gilts grown from 24 to 120 kg bodyweight.

EXPERIMENTAL PROCEDURE

All animals were the F1 hybrid cross from PIC Camborough 15 gilts X Canabrid boars. At about 18 kg bodyweight, 29 gilts and 29 barrows were selected for the experiment. The pigs had ad libitum access to a grower diet from 24 to 65 kg, and to a finisher diet from 65 to 120 kg (Table 1). These diets contained essential amino acids, minerals and vitamins at levels deemed to not limit lean tissue growth when consumed at or above 90% of the NRC feed intake predicted curve.

Pigs were sacrificed as follows: four barrows and four gilts at 24 (± 2) kg bodyweight, and five barrows and five gilts at each of the following weights (± 2 kg): 56, 72, 88, 104 or 120 kg bodyweight.

Individual bodyweight and feed disappearance data were recorded weekly and prior to slaughter. Upon reaching its target slaughter weight, each pig was euthanased. The contents of its stomach, small and large intestines, gall bladder and urinary bladder were emptied. Empty whole body composition was then defined as the weight of the carcass and viscera after the contents of the latter were emptied.

Each frozen carcass and viscera were ground together in a meat grinder and mixed thoroughly. Sub-samples of each carcass and viscera mix were then freeze-dried to estimate moisture content. Dried samples were analyzed for nitrogen, ether extract, ash and moisture content.

Protein and lipid deposition rates were predicted for barrows and gilts, separately, using a variety of statistical curve-fitting techniques. Comparisons for average daily weight gain, feed intake and feed efficiency between each slaughter weigh group, gender and their interaction were made using a statistical software package (SAS, 1987).

RESULTS AND DISCUSSION

Feed intake for pigs grown between 24 and 56 kg bodyweight was lower than expected. Feed intake was considered adequate to support the targeted levels of growth for pigs grown above 56 kg bodyweight. Interestingly, there was no difference (P > 0.10) in average daily feed intake and feed/gain ratio between gilts and barrows (Table 2).

The form of the protein deposition curves was different for barrows and gilts (Figure 1). At 24 kg bodyweight, the protein deposition rate was 137 and 98 g/d for barrows and gilts, respectively. Protein deposition rate increased after 24 kg bodyweight, reached a peak, and proceeded to decline towards 120 kg bodyweight when the rate of protein deposition was 100 and 137 g/d for barrows and gilts, respectively.

Peak protein deposition was calculated as 150 g/d between 43 and 52 kg bodyweight and 133 g/d bodyweight between 68 and 74 kg bodyweight, for barrows and gilts, respectively. Protein deposition for barrows was less than for gilts after about 87 kg bodyweight because of a continual increase in their rate of lipid deposition towards 120 kg bodyweight (Figure 2).

IMPLICATIONS

These results reinforce the need for split sex and multiply phase feeding systems for pigs grown to market. As a consequence of the different patterns and rates of protein and lipid deposition for gilts and barrows, different nutritional recommendations, particularly for essential amino acids and energy, are necessary to minimize feed costs and maximize carcass quality.

This study has provided information concerning how protein deposition changes as pigs of this genotype grow. As protein deposition is the major determinate of the essential amino acid requirement, recommendations for these amino acids may be made to meet these levels of protein deposition.

Table 1. Experimental growing and finishing diets (as fed, %)

Figure 1. Protein deposition rate curves of barrows (- - -) and gilts (¾) grown from 24 to 120 kg bodyweight

Figure 2. Lipid to protein deposition ratio curves of barrows (- - -) and gilts (¾) grown from 24 to 120 kg bodyweight

Table 2. Average daily rates of weight gain for whole body carcass,
feed intake and feed:gain ratio for gilts and barrows at six consecutive bodyweights
between 24 and 120 kg.

ACKNOWLEDGMENTS