Abstract

<jats:p>
Porcine somatotropin (pST) treatment of pigs consistently improves average
daily gain (ADG) and feed conversion ratio (FCR). However, most studies have
been conducted with individually housed pigs, of unimproved genotype and over
a lighter finisher phase than current practice. The present study was designed
to determine whether a commercial pST (Reporcin) treatment regime would
improve growth performance in heavy boars and gilts (initial weight 79 kg) of
an improved genotype and housed under commercial conditions. The 2 2
factorial experiment involved 160, 19-week-old Large White Landrace pigs (80
males and 80 females) in 20 pens of 8 pigs/pen. The respective factors
were sex (boars and gilts) and dose of pST (0 and 5 mg/day). Pigs were fed
a wheat-based diet formulated to contain 200 g crude protein, 10.2 g available
lysine, and 14.6 MJ DE/kg to ensure that responses to pST and sex were
expressed. Injections of pST were given daily for 28 days prior to slaughter
using a commercial applicator designed for this purpose. Pigs were bled by
venipuncture on days 7 and 28 of treatment and the plasma samples analysed for
plasma urea nitrogen (PUN) and glucose. The degree of stomach ulceration at
slaughter was assessed by a veterinary pathologist. Daily pST treatment
increased ADG (P = 0.003), particularly in gilts,
as indicated by the interaction (P = 0.015)
between sex and pST. Thus, gilts treated with pST grew 23% faster than
control gilts (1093 v. 1273 g/day), whereas the
pST-treated boars grew only slightly faster (+2.5%) than control
boars (1261 v. 1291 g/day). Feed intake was similar
for boars and gilts and was decreased in both sexes by 10% during pST
treatment. FCR was higher in control gilts than in boars and was improved by
pST treatment. This was particularly evident in the gilts such that there was
no difference in the FCR of pST-treated gilts and boars. Back fat at slaughter
was reduced by 2.3 and 3.2 mm in boars and gilts treated with pST,
respectively. The only stomach lesions observed were very minor in severity
and there was no effect of pST on the proportion of pigs exhibiting stomach
ulcers (7/80 and 9/79 for control and pST-treated pigs, respectively;
χ2 = 0.31, P =
0.58) or visible possible injection site lesions (0/80 and 1/79;
χ2 = 1.01, P =
0.31). The PUN response mirrored the effects of sex and pST on FCR. Indeed,
there was a high correlation (R = +0.84,
P &lt; 0.001) between FCR and PUN. In conclusion, pST
treatment of finisher pigs of an improved genotype and housed under simulated
commercial conditions improved growth performance, decreased back fat, and
negated sex differences.</jats:p>