The effect of rate of gain during the growing and finishing periods on the feed efficiency and carcass composition of the pig: II. Contrasting patterns of growth produced by different rates of gain from 20 to 55 kg and 55 to 87 kg live weight

SUMMARY Pigs were grown at controlled rates of live-weight gain from 20 to 55 kg and from 55 to 87 kg live weight, at which weight they were slaughtered. Six growth-rate treatments were compared and were referred to as High-High (HH), High-Moderate (HM), High-Low (HL), Moderate-High (MH), Moderate-Moderate (MM) and Low-High (LH). The right-hand side of each carcass was divided into the four primary jointsand each joint was physically dissected into bone, skin, subcutaneous fat and lean meat. The boneless tissue of each joint was analyzed for moisture, ether extractable fat and nitrogen. It was found that an increase in the rate of live-weight gain in the first growth period, tended toimprove the efficiency with which feed was converted into live weight. In the second growth period the efficiency of feed conversion was dependent on the rate of gain both in that period and in the preceding period. Restricted growth in the first period improved the efficiency of feed conversion both in the second period and over the entire experimental period compared with rapid early growth. The implications of compensatory growth are discussed. There was no treatment effect on carcass length, but hindleg length and ham circumference measurements showed that the proportion of gammon in the side was lower in the HH pigs compared with the other five treatments. This was confirmed by the weight of the gammon joint expressed as a percentage of the trimmed side. There was also a decrease in the proportion of shoulder and an increase in the proportion of middle in the HH pigs. Differences between the other five treatments were small. The changes in conformation were due largely to the effect on fat distribution throughout the side particularly in the gammon and back regions. The HH treatment resulted in a significant increase in the percentage fat in the side compared witheach of the other five treatments. Within these five treatments there was no significant difference in the percentage fat in the side. This suggests that equal importance may be attached to the rate of live-weight gain in both the growing (20–55 kg) and finishing (55–87 kg) periods in determining the fatnessof the bacon weight carcass. The treatments had little effect on the chemical composition of the fat-free boneless meat. The results are discussed in relation to current growth theory.