During the grow-finish period, body weight gain is mainly a combination of lean muscle and fat deposition. As pigs get older, the composition of weight gain shifts from lean muscle deposition to a larger proportion of fat deposition. However, it requires more energy to deposit fat than muscle, and thus feed efficiency decreases as pigs get heavier (Stender, 2012). Therefore, understanding the genetic correlations among lean and fat deposition with weight gain in different stages of growth will help us to select pigs with more efficient lean gain.

Genesus has recorded individual feed intake, growth rate, and ultrasound fat and loin depths since 2004. Ultrasound backfat and loin depth have been collected on individual pigs near 80kg and 120kg body weights. Such information enables us to estimate the heritability and correlations among the component traits of efficient lean gain including average daily feed intake (ADFI) during 70 – 120kg, days to 120kg (Day120), backfat depth (FD120) and loin depth (LD120) at 120kg bodyweight.

In order to have a better understanding of efficiency in different growth stages, we estimated the genetic correlations between the lean gain component traits and days to 80kg (Day 80) and average daily gain during 80kg – 120kg (ADG) (Table 1).

Day 120 has very high genetic correlations with growth rate in all stages, which means selection on Day 120 is an efficient way to genetically improve growth rate. Compared with ADG (h2 = 0.05), Day 80 has much higher heritability (h2 = 0.17) and higher genetic correlation with Day120, indicating selection on Day 120 may result in faster genetic improvement for growth to 80kg (Day 80) compared to later growth (ADG).

Following a long-term emphasis on selection for Day 120, Genesus pigs have obtained very good genetic potential for fast growth. The question is, can we improve growth rate and efficiency even further?

Alternative strategies to drive growth rate improvement may exist, and we hypothesize that by placing selection emphasis on both Day 80 and ADG may increase the overall growth rate to 120kg. Additionally, our feed intake testing focuses on the ADG period. Combining ADFI, Day 80, and ADG with the ultrasound fat and loin depth measures will allow us to enhance feed efficiency improvement during this period. Thus, the end result would be selection of pigs with more efficient lean gain over the whole grow-finish period, especially in the later period.

Genesus continually focuses on enhancing our genetic improvement program by considering such important alternative strategies. Improving lean gain efficiency for Genesus customers will contribute significantly to the Genesus goal of improving customer profitability.