The effect of energy intake on development and reproduction of gilts and sows

<p/>The rate of reproduction in female pigs is an important trait with regard to pig production. Reproduction may be defined as the number of piglets reared per sow per year. This trait is dependent on age at puberty, conception rate, litter size, the interval from weaning to oestrus and the longevity of the sow.<br/>Heritability of many of the reproductive traits is low. Therefore, the effects of environment are very important with respect to factors that contribute to the variation in these traits. Nutrition can make an important contribution to these environmental factors. The effect of energy intake on a number of reproductive traits in female pigs was investigated. Results of studies on the influence of level of nutrition on reproductive traits reported since 1950 were analysed statistically (chapter 1). It was concluded that an increase in ovulation rate after a short or long period of high energy intake is not systematically associated with an increase in litter size. Embryonic mortality may be increased, especially if the high energy intake is maintained during the first month after conception. In addition, it was concluded that the influence of energy intake during rearing on reproductive traits had not been studied sufficient enough to arrive at clear conclusions.<p/>The importance of post weaning feeding level on consecutive reproduction was studied in 113 primiparous Dutch Landrace sows (chapter 2). Feeding levels applied during the interval from weaning to oestrus were 4 and 2.5 kg per sow per day, respectively. Results showed that within 21 days after weaning the percentage of sows with spontaneous oestrus were 65 and 53, at the high and low feeding level, respectively.<br/>The interval from weaning to spontaneous oestrus and the ovulation rate were not different. In addition size of uterus and ovaries were not affected by feeding level. Ovulation rate was not related to weight at weaning and weight at oestrus nor to weight loss during lactation, weight gain during the interval from weaning to oestrus or size of the previous litter at birth. It was concluded that a high feeding level in primiparous sows after weaning may be important with regard to the condition of the sow and to advance oestrus.<p/>From literature results and the previous experiment it was decided to study the effect of energy intake during rearing on reproductive rate.<br/>A large scale experiment was conducted with gilts. A total of 680 gilts from the age of 12 weeks was assigned to one of the four energy levels that were tested. The energy levels were about 3 M, 2.5 M, 2.1 M and 1.8 M in which M is the metabolizable energy required for maintenance (treatments 1, 2, 3 and 4, respectively). The protein allowance was dependent on the weight of the gilts and was similar for all treatment groups. The rations were prepared by mixing two basal feeds in different ratios. Two balance trials (determination of energy and N in feed, faeces and urine) with 16 gilts of 35 kg and 16 gilts of 64 kg were first carried out (chapter 3). The digestibility of energy was not influenced by the different treatments. Digestibility of crude protein and crude fibre increased in the treatments in which energy intake was reduced (p< 0.0 1). Metabolizable energy content of the ration was not affected by the level of energy intake. Protein and fat deposition were calculated from the rate of gain and the daily energy intake. Protein deposition, at the same amount of digestible protein intake, was reduced at a level of energy intake of 2.1 times the energy required for maintenance or less. However, fat gain was much more reduced than protein gain when energy intake was diminished.<br/>The four energy levels were applied from 12 to 38 weeks of age (chapter 4). Each gilt received 2.5 kg per day from 38 weeks of age. Gilts without oestrus before the age of 38 weeks were induced.<br/>A total of 290 gilts was kept to produce their first litter, while in 224 gilts the ovulation rate was determined (chapter 5). More gilts needed to be culled at the two higher levels of energy intake as compared to the lower levels of energy intake. The number of gilts with spontaneous oestrus was not affected by the level of energy intake. Age and weight at first oestrus increased and decreased, respectively, as energy intake during rearing was reduced (chapter 4). It was concluded that age at puberty will be determined more by age than by weight. However, fatness of the body acts as a threshold for reaching puberty at a high level of energy intake (>, 2.5 M). Conception rate was lower at the two higher levels of energy intake than for gilts at the two lower levels. Embryonic survival and number of piglets born were not affected by energy intake. In addition the average birth weight and the homogeneity of the litter were also not affected by energy intake.<br/>More gilts responded to the induction of oestrus with PG600 at the two lower levels of energy intake than at the two higher levels of energy intake. Gilts inseminated at an induced oestrus had a similar litter size compared to gilts inseminated at a spontaneous oestrus. However, the average birth weight of the piglets and the homogeneity of the litter were reduced.<p/>The difference in number of piglets born alive in the first litter between a herd of 100 gilts with a high level of energy intake during rearing ( ≥2.5 M) and a herd with a low level of energy intake (2.1 M or 1.8 M) was on the average 103.<br/>Preliminary results of further experiments show that the number of piglets born in the following parities did not differ between the treatment groups. The differences in backfat thickness which were found at first parturition seemed to have disappeared at the second parturition. In view of the cost of the feed consumed and the reproductive performance an energy intake during rearing of 2.5 times maintenance or more is unfavourable, when adequate protein is given.