Date Full Report Received02/10/2016
Date Abstract Report Received02/10/2016
Funded ByNational Pork Board
Feed efficiency and immune response of market hogs can have a profound effect on the profitability of pork producers. Therefore, we examined the impact of the newly isolated hormone, GnRH-II, on feed efficiency and immune function of growing/finishing pigs. The objectives of our study were: 1) Determine GnRH-II levels in growing/finishing pigs provided either a feed-restricted or ad libitum diet and 2) Examine the influence of GnRH-II on immune function in growing/finishing pigs. Terminal cross barrows were weaned, moved to nursery facilities at 21 days and fed standard Nursery I and II diets for 6 weeks. Next, pigs were provided ad libitum access to Phase I of a 3-phase grower/finisher diet, commonly used at the University of Nebraska-Lincoln swine unit, for 4 weeks. During the last week of the Phase I diet, barrows were randomly allocated to receive either an ad libitum or restricted (50% of ad libitum) intake diet, placed in individual pens with ad libitum access to water and allowed a 7-day acclimation period. Daily feed intake was steadily increased in an attempt to determine the average ad libitum feed intake. Next, pigs were provided the Phase II diet and feed intake treatments were initiated, with half of the daily feed provided in the morning and evening. However, after Week 1, barrows fed the restricted intake diet exhibited significant weight losses. To avoid any potential health issues related to weight loss, we adjusted the restricted intake diet to 68% of ad libitum for the remainder of the study. Pigs received the Phase II and III diets for 4 weeks each. At the start of Week 2 for each feeding phase, animals received diets mixed with 0.4% titanium dioxide, to estimate the ability of pigs to digest feed, for 10 days. On Day 8 – 10, 3 fecal samples were taken from each barrow (8 am and 5 pm), pooled within pig, and examined for nitrogen, phosphorus, titanium dioxide and energies. Barrows were weighed weekly and blood samples taken every 2 weeks to measure blood levels of GnRH-II and a marker of the immune response. Overall, ad libitum fed growing/finishing pigs were heavier, had greater average daily gain and average daily feed intake, and exhibited decreased gain:feed ratios compared to restricted fed pigs. Despite no differences during Phase II, dry matter and nutrient digestibility were greater in restricted pigs compared to ad libitum pigs in Phase III. Serum GnRH-II concentrations were relatively low and varied significantly among animals prior to treatment. Although GnRH-II levels were lower for barrows fed a restricted vs. ad libitum diet on Day 7 and 14, we did not detect an overall effect of dietary treatment. However, GnRH-II concentrations did decrease with age regardless of treatment. No differences in immune response between treatments were observed through Day 42 of the trial, although the immune response tended to be decreased on Day 7 in barrows fed the restricted diet, likely associated 2 with severe weight loss from a 50% feed restriction during the first week of the trial. Based on results from this study, we were unable to link GnRH-II levels with feed efficiency or immune response in growing/finishing barrows. However, we did determine that GnRH-II levels vary among animals and decrease with age during the grower/finisher stage, suggesting that it may be a potential marker for growth.