Introduction

Despite years of breeding for specific characteristics, variation still exists within our population of pigs with respect to growth, feed intake and feed efficiency. This trial is part of a series of experiments designed to improve our understanding of energy metabolism in growing and finishing pigs.

The overall objective of this experiment was to determine if early growth rate (potential growth rate, PGR) is predictive of efficiency of energy utilisation later in life. Understanding the differences in energy utilisation among fast and slow growing pigs will help us to manage and develop cost-effective feeding programs that most closely meet the specific requirements of these groups of pigs.

Materials and Methods

* "Segregating pigs and feeding based on potential growth rate does not improve the ability to match feed to requirements"

Sixty barrows were assigned to either a slow, average or fast PGR group based on growth rate from birth to nursery exit. When the pigs reached 30kg bodyweight, they were placed in individual pens and assigned to receive either a low- or a high-energy diet at 100 or 85 per cent of ad libitum intake. The experiment therefore, had a total of 3×2×2 = 12 treatments, (three growth potentials, two dietary energy concentrations and two intake levels).

Diets are described in Table 1. The high-energy diet had more wheat and canola oil and less barley than the low-energy diet. Diets were formulated with a comparable standard ileal digestibility (SID) per cent lysine, therefore the lysine/energy ratio was lower in the high energy diet. Lysine, however, was formulated to be non-limiting in both rations. Diets contained 0.4 per cent celite, a source of acid-insoluble ash used as a marker for digestibility calculations.

The pigs were slaughtered when they reached 60kg bodyweight, the carcasses ground and analyzed for nutrient content. Comparing the data with a group of pigs slaughtered at the beginning of each experiment allows the calculation of nutrient retention within each growth period. Dietary NE was calculated as RE + FHP where RE = energy retained in the carcass and FHP = fasting heat production estimated as 179kcal per kg BW^0.6 (Noblet et al., 2003).

Faeces were collected throughout the growing period to allow for the measurement of DE and estimation of NE using the equations developed by Noblet (2004) and the CVB (2005) which are predictive equations based on nutrient content and digestibility.

Results

The pigs were selected for PGR based on growth rate in farrowing and nursery. The targeted body weight to begin the experiment was 30kg for all pigs, therefore pig age differed. The slow-growing pigs were about 98 days of age, almost four weeks older than the fastest growing pigs, who had reached 30kg bodyweight at only 71 days of age. The average PGR group was 78 days of age. Despite this, average daily gain from 30 to 60kg bodyweight was only slightly higher for the fast PGR pigs. A lower daily feed intake for these pigs resulted in a tendency for an improved feed efficiency (P=0.07; Table 2). Energy concentration of the diet had no effect on growth rate; feed intake was reduced on the high-energy diet, therefore feed efficiency (kg/kg) was improved for pigs fed this diet.

As expected, pigs fed the diet at 100 per cent had improved growth relative to pigs allowed only 85 per cent of ad libitum. Feed efficiency (kg/kg) was also improved at the higher feed intake.

The efficiency of utilisation of energy for growth, protein or lipid deposition was numerically lower for the fast growing pigs than the average or slower growing pigs; however, this difference was not significant (Table 3). The efficiency of energy utilisation for protein or lipid deposition (g per Mcal intake) was improved with the low-energy diet. Pigs fed the diet at 85 per cent ad libitum utilised energy more efficiently than those allowed 100 per cent intake, regardless of PGR or dietary energy concentration. The ad libitum fed pigs had fewer days to reach 60kg, grew faster, ate more and had improved feed efficiency. However, the efficiency of energy utilised for protein or lipid deposition was improved with the lower intake.

The experimental DE and NE values obtained are shown in Table 4. The DE content of the diets was much lower than expected.

The authors do not have an explanation for this. These diets were representative of others they have used and energy digestibility was higher. The NE values calculated using the INRA (French) equation were similar to the formulated NE concentration. The values used in our formulations are largely obtained from the INRA data base so this is evidence that this database is useful for feedstuffs obtained in Western Canada.

Conclusions

The efficiency of the utilisation of dietary energy for growth was comparable among pigs selected for high or low potential growth rate. This implies that segregating pigs and feeding based on PGR is not a tool that will improve our ability to match feed to requirements.

Acknowledgements

Strategic funding provided by Sask Pork, Manitoba Pork Council and Saskatchewan Agriculture and Food Development Fund. Funding specifically for this project from the National Sciences and Engineering Research Council of Canada (NSERC) and Cargill is gratefully acknowledged.

September 2012