A total of 1,360 pigs (PIC 337 × 1050, initially 53.0lb) were used in a 125-day study to determine the effects of dried distillers grains with solubles (DDGS) withdrawal post-immunocastration (IC; Improvest, Pfizer Animal Health, Kalamazoo, Michigan) on growth performance and carcass fat quality of growing-finishing pigs, reported M.D. Asmus and colleagues at Kansas State University in their paper presented at Kansas State University Swine Industry Day 2012.

Pens of pigs were randomly allotted by initial weight and gender (barrows or IC) to one of three dietary treatments with eight replications per treatment for a total of 48 pens with 27 to 29 pigs per pen.

Treatments were arranged in a 2×3 factorial with the main effects of gender (barrow or IC) and diet (zero DDGS throughout, 30 per cent DDGS throughout or 30 per cent DDGS to day 75 then withdrawn to zero to day 125).

Boars were injected with Improvest on days 39 and 74 of the study.

Dietary treatments were corn-soybean meal– based diets and fed in five phases.

No gender × diet interactions (P>0.18) were observed except for a tendency for feed:gain ratio (P<0.07) during the second phase (days 25 to 53), when one of the two barrow groups fed 30 per cent DDGS had an increase in average daily feed intake resulting in poorer feed:gain ratio. For the entire period before the second Improvest injection (days 0 to 74), barrows tended (P<0.08) to have increased average daily gain (1.98 versus 1.95lb) and increased (P<0.001) average daily feed intake (4.32 versus 3.91lb) but were less efficient (P<0.001) than boars (2.19 versus 2.01). During the same time period, pigs fed 30 per cent DDGS had reduced (P<0.002) average daily gain and poorer feed efficiency.

For the period after the second Improvest injection until the first marketing event (days 74 to 107; 33 days after the second dose), IC pigs had increased (P<0.01) average daily gain (2.29 versus 2.10lb), similar average daily feed intake (6.92 versus 6.81lb) and were more efficient (P<0.001; 3.02 versus 3.25) than barrows. From days 0 to 107, IC pigs had improved (P<0.03) average daily gain (2.05 versus 2.01lb), feed:gain ratio (2.34 versus 2.52) and lower average daily feed intake (4.80 versus 5.06lb) than barrows. The inclusion of 30 per cent DDGS, regardless of withdrawal or gender, did not influence average daily gain or average daily feed intake but did worsen (P<0.001) feed efficiency.

For the period after the second Improvest injection to the end of the trial (days 74 to 125; 51 days after the second dose), IC pigs had increased (P<0.01) average daily gain (2.29 versus 2.10), average daily feed intake (7.09 versus 6.82) and were more efficient (3.09 versus 3.25) than barrows. Overall (days 0 to 125), IC pigs had improved (P<0.003) average daily gain (2.07 versus 2.02) and feed:gain ratio (2.44 versus 2.58) and lower average daily feed intake (5.05 versus 5.22) than barrows. The inclusion of 30 per cent DDGS, regardless of withdrawal or gender, again did not influence average daily gain or average daily feed intake but worsened (P<0.001) feed efficiency.

Carcass yield was lower (P<0.001) for IC pigs than barrows regardless of dietary DDGS or withdrawal strategy. Pigs fed 30 per cent DDGS throughout had decreased (P<0.001) carcass yield; however, withdrawing DDGS from the diet on day 74 was effective at fully recovering the yield loss, returning values similar to that of pigs fed the control diet throughout.

Carcass fat iodine values were consistently higher (P<0.001) regardless of fat depot or harvest time when 30 per cent DDGS were included in the diet. The withdrawal strategy was successful at lowering (P<0.003) iodine value when compared to feeding DDGS throughout; however, it was not successful (P<0.001) at fully lowering iodine value to values similar to pigs fed the control diet throughout. Iodine value of the jowl (P<0.07), loin (P<0.02) and clear plate (P<0.003) tended to be or were greater for IC pigs than barrows on day 107 but differences in iodine value between IC and barrows disappeared by day 125. Similar to previous studies, withdrawing DDGS from the diet before harvest can improve carcass fat quality (iodine value) and recover yield loss but feed:gain ratio was still poorer regardless of withdrawal strategy.

Overall, the KSU group noted that immunocastrates had reduced carcass yields but they also had reduced average daily feed intake and improved average daily gain, which led to improved feed efficiency.

Although the use of Improvest can increase iodine value of fat depots when pigs are harvested at a shorter interval after the second injection, extending the feeding duration after the second injection returns iodine value to values similar to barrows.

Another interesting observation made by Asmus and co-authors is the magnitude of changes in fatty acid profile or iodine value between the different fat depots in relationship to rations, genders and days after second injection with the immunocastrated barrows exhibiting larger changes than the contemporary physically castrated barrows.

Reference

Asmus M.D., M.D. Tokach, S.S. Dritz, J.L. Nelssen, R.D Goodband and J.M. DeRouchey. 2012. The effects of immunocastration and dried distillers grains with solubles withdrawal on growth performance, carcass characteristics, fatty acid analysis, and iodine value of pork fat depots. Proceedings of the Kansas State University Swine Industry Day 2012, p218-248.

Further Reading You can view the full paper in the proceedings by clicking here. Other papers presented at this conference can be viewed by clicking here.

January 2013