Effects of two levels of feed allocation on IGF‐I concentrations and metabolic parameters in GnRH‐immunized boars

Abstract

Immunocastration of boars leads to a maintenance of growth harmone (GH) and a loss of anabolic hormones [androgens, oestrogens, insulin-like growth factor (IGF-I)] but an increase of voluntary feed intake. The aim of the experiment was to clarify whether IGF-I is increased by increasing feed supply in immunocastrated boars leading to improved anabolism. Two groups of six boars were given 2 or 3 kg of feed (13.5 MJ ME/kg) daily from 18–28 weeks of age. Because in boars feed intake is limited by gonadal hormones, a group with further increased feed supply could not be included. Until week 22 (second vaccination) gonadal steroids in blood were normal but dropped rapidly thereafter. Growth harmone levels did not change following vaccination. Pigs allocated 3 kg feed had 28% higher circulating IGF-I after the second immunization compared with pigs fed 2 kg feed daily. Higher IGF-I was associated with increased weight gain (682.4 g/day vs. 466.7 g/day; p < 0.01) and protein synthesis ((13)C-leucine infusion; 405 g/day vs. 247 g/day, p < 0.01). Protein breakdown (urea) was not different. Body fat (D(2)O) decreased in the low feed group from 15.2% (week 19) to 6.1% (week 25). In the high feed group it remained at the level found before second vaccination (13.7% vs. 15.0%). It is concluded that in the phase of reduced testicular steroids which inhibit appetite it is possible to increase feed intake which in turn increases IGF-I and protein deposition without accumulating excessive fat.

Effect of high dietary fat content on heat production and lipid and protein deposition in growing immunocastrated male pigs

“…Moreover, higher N losses with urine observed in the present study due to IC/growth effect as a consequence of higher feed (and N) intake at similar daily N gain indicate that daily N or protein content in the diet should be reduced with growth and IC. In agreement, plasma urea N concentrations was shown to increase in IC pigs within the 1 st week after V2 (Claus et al, 2007;Bauer et al, 2009) or shortly after indicating increased amino-acid catabolism. These results confirm that CP content of the diet for IC could be decreased after V2 to reduce unnecessary N emissions.…”

The effect of immunization against GnRF on nutrient requirements of male pigs: a review

“…This increase in PUN is associated with the timing of the decrease in testicular activity as measured by plasma testosterone. Plasma IGF-I, which has been shown to be positively related to previous growth rate, decreased more gradually in immunized pigs and did not reach a plateau until beyond 14 days after the second immunization (Metz and Claus, 2003;Claus et al, 2007;Bauer et al, 2009). Plasma leptin concentration was increased at 14 and 28 days after immunization against GnRF , possibly in response to increased feed intake and fat deposition that occurs around this time.…”

“…This suggests that changes in protein metabolism occur very quickly. Indeed, when feed intake was restricted to either 2 or 3 kg/day, there was a rapid increase in PUN between 8 and 10 days after the second immunization (Bauer et al, 2009). This increase in PUN is associated with the timing of the decrease in testicular activity as measured by plasma testosterone.…”

“…This is a result of either increased protein intake, decreased lean tissue deposition or both. The temporal studies of Claus et al (2007) and Bauer et al (2009) indicate that PUN begins to increase within the first few days after immunization, before any increase in feed intake. This suggests that changes in protein metabolism occur very quickly.…”

“…Antibody titres to GnRF peak a week after the second dose and gradually decline over the next 8 weeks or longer (Claus et al, 2007;Dunshea et al, 2008;Bauer et al, 2009). The intensive studies of Claus et al (2007) and Bauer et al (2009) show that plasma androstenone, testosterone and LH had all reached a nadir 6 to 10 days after the second immunization. Similarly, plasma urea nitrogen (PUN), an accurate proxy for excess amino acid catabolism, was found to be increased at 14 and 28 days after immunization against GnRF .…”