|
Animal Science Departmental Report 2004-2005 Return to Swine articles
Genetic by Production
Environment Interactions M. T. See Introduction Continuous genetic improvement is occurring within the pork industry. However, the commercial production environment does not always allow pigs to express their full genetic potential. This may be due to a variety of factors including health, nutrition, production environment, stocking density, and ambient temperatures. The intent of this project was to allow pigs sired by different genetic lines to express their full genetic potential, as well as, the genetic potential that is expressed in the commercial setting. This reports details the comparative data for maximum potential and expected potential while controlling for genetic line of the sire, sex and production environment in the statistical model. Birth and Pre-weaning Data: Sows (DK43) were mated at a commercial swine operation. Number of sows mated to each sire line and the resulting reproductive data are summarized in Table 1. All pigs (n = 1438) were individually weighed at birth, and each pig was doubled ear tagged with a colored tag denoting sire line and a unique identification number. Pigs were weaned at three weeks of age. Pigs were infected with PRRS at the sow farm prior to weaning. A very high level of cross fostering was observed as denoted by movement of pigs with ear tags across sows and across farrowing rooms and buildings. Cross fostering is believed to have contributed to the extent and severity of the PRRS infection. At weaning pigs were transported to NCSU – Swine Evaluation Station and the remainder were placed in three commercial nurseries. The standard commercial feeding program was followed at both locations. A performance evaluation was conducted only at NCSU through the nursery phase. The finishing phase of the study occurred at both the commerical location and on the NCSU – Swine Evaluation Station. At NCSU 400 pigs were available for placement. Pigs identified as unthrifty, unhealthy, or having severe lameness or hernias were eliminated from further evaluation. From the remaining pigs, 336 (56 of each sire line and sex combination) were randomly selected and allocated four to a pen. A total of 559 pigs were delivered from the three nurseries to the commercial finisher. Twenty-one pigs were eliminated from the study and pigs were randomly assigned to pen within sire by sex line combination. Pens contained 20 to 22 pigs and there were 12, 7, and 7 pens of Line 1, Line 2, and Line 3 pigs, respectively. Again, pigs at both locations received the same feeding budget and all diets were made at the commercial mill. No pigs on this study received Payleanâ during finishing. All pigs at NCSU were real-time scanned for backfat depth and loin eye area at finisher placement (4 pigs per pen). At the commercial site 10 pigs were randomly selected from each pen at placement and the same ten pigs were scanned throughout the study. Pig weights and real-time data were collected at intervals of approximately 50 pounds. Feed allotment was recorded daily by pen at both locations. Feed was estimated at the commercial site and weighed back (NCSU) at the end of each period. During period 4 pigs suffered from unusually hot weather and a 2% mortality rate was observed at NCSU for this period resulting in an overall mortality rate of 2.7% (n=9). Overall finisher mortality at the commercial site was 3.7%. Results and Discussion Resulting nursery mortality at NCSU was 4.7%. Nursery mortality rates were 3.6, 7.1, and 3.6% for Line 1, Line 2, and Line 3 sired pigs, respectively. Birth weight of all pigs and weaning weight and pre-weaning average daily gain for those transported to NCSU are summarized in Table 2. Statistical models for birth and pre-weaning data included fixed effects of sire line and sex there was no significant interaction of sire line * sex. Barrows tended (P = .07) to have a greater average daily gain then gilts, .367 vs. .352 ± .006. Covariates were included in statistical models for birth weight and weaning weight as parity of dam and parity of dam and weaning age, respectively. For each successive parity birth weight increased .05 ± .01 lbs (P < .001) and weaning weight .1 ± .05 lbs (P < .001). Each additional day of age at weaning resulted in .25 ± .04 lbs (P < .001) weaning weight per pig. Results indicate that Line 1 sired pigs were heavier at birth and weaning and had a high pre-weaning average daily gain than Line2 or Line 3 sired pigs. Nursery Phase:Nursery performance is summarized in Table 3. The Line 1 sired pigs were heavier at placement and this advantage in size translated to greater feed intake and average daily gain, resulting in heavier weights after the first three weeks. However, no differences were observed between sire line groups during later periods or for overall nursery performance. Finishing Phase: Finishing data would indicate that the Line 1 and Line 3 sired pigs were consistently heavier and faster growing than Line 2 sired pigs. After 200 pounds the Line 1 sired pigs had the greatest loin eye area. Line 3 sired pigs had a significantly higher average daily feed intake, were less efficient and were fatter at every scan period than Line 1 and Line 2 sired pigs. Across production environments pigs at NCSU grew 30% faster and consumed 27% more feed on a daily basis resulting in a 27% greater lean gain per day. The genetic line by environment interaction indicates that the Line 3 sired pigs were the highest in feed intake in both production systems but that the Line 1 sired pigs consumed more feed than the Line 2 sired pigs at NCSU. Possible causes of this interaction may include stocking density, pig to feeder space ratio, and pig to water ratio or environmental quality. A genetic line by production environment interaction was also observed for overall gain to feed ratio where the Line 1 and Line 2 sired pigs were more efficient in the NCSU production environment but the Line 3 pigs did not differ in efficiency across environments. For lean efficiency the Line 1 and Line 2 sired pigs did not differ across production environments but the Line 3 sired pigs were the least efficient in the NCSU production environment. No difference for lean efficiency was observed between barrows and gilts in the commercial production environment but gilts were significantly more efficient than barrows in the NCSU environment. ConclusionThese results indicate that production environment can limit the pigs ability to express it’s genetic potential. In addition, genetic line by production environment interactions may occur that cause animals differing in genetic composition to rank differently under different conditions.
Table 1. Summary of breeding and piglet production data.
Table 2. Commercial Sire line differences on birth weight and pre-weaning performance.
Table 3. Least squares means by sire line for nursery performance at NCSUa
a Means with different superscripts were significantly different P < .10.
Table 4. Least squares means by production environment (E), sire line (G), and sex (S) for finishing performance by period.
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||