Factors affecting ovulation and embryo quality in pigs
The age at which gilts could be effectively induced into a precocious puberty was assessed by injecting gilts of different ages (100-180 days old) with an exogenous gonadotrophin (PG600). Gilts could be stimulated into puberty as early as 100 days old but they had to be at least 160 days old to maintain cyclicity. Ovulation rate (OR) was found to increase with increasing age. Gilts of two different ages (160, 180 days old at induction) were fed two different diets (lysine:DE (g/MJ DE) ratios 0.3 and 0.9) over a 6 week rearing period. At puberty induction the low protein (LP) gilts were lighter and fatter than their HP counterparts (backfat probes, 12.0 vs 10.4 (P<0.05) respectively; eye muscle depths, 67.4 vs 71.2 respectively (P<0.05)). Response to gonadotrophin injection was significantly reduced in the LP gilts. OR was also significantly lower in the LP gilts (15.9 ± 1.6 vs 21.4 ± 1.4; P<0.01). The factor having most effect on OR was protein gain over the rearing period. In a third experiment, cycling sows of three different parity categories were fed a protein free (PF) diet over one oestrous cycle. PF Sows had a tendency to have reduced follicle counts and reduced subsequent interval from standing oestrus to ovulation (45.2 hours vs 55 hours). The effect of feeding a high fibre diet (50% unmolassed sugar beet pulp) to gilts over the rearing period on reproductive performance was also assessed. In the first experiment gilts exposed to boar stimulation alone only showed puberty response within 40 days and this response was positively correlated with weight. Gilts induced with exogenous gonadotrophin responded within 10 days and showed an OR response to weight. There was no effect of diet on OR. In the second experiment, there again was no effect on OR. Cell counts of the embryos collected from the high fibre gilts and cultured were significantly higher than the controls (198 ± 7 vs 138 ± 9; P<0.005) at 6-7 days; this was taken as an indication that feeding a high fibre diet may improve embryo survival.