ABSTRACT
Two experiments were conducted at the piggery unit of the Department of Animal Science Farm, University of Nigeria, Nsukka, from July 2007 to March 2009, to determine the effect of nutrition and body condition at first mating on the reproductive performance of gilts. The first experiment evaluated the effects of feeding different combinations of protein and energy diets on age at onset of first observed oestrus, growth rate, backfat reserve and body condition score of the gilts from weaning to puberty. Fifty-four (54), eight week old weaner gilts were used for this trial. They were randomly assigned to nine experimental treatment diets having different combinations of protein (16%, 18% and 20% crude protein) and energy (2800 kcal/kg, 3000kcal/kg and 3200kcal/kg) with six (6) gilts per treatment. The gilts in each treatment were housed in pairs making up three (3) replicates per treatment. Estrus detection was carried out twice daily at 0800hr and 1600hrs in the presence of mature boar beginning from the age of five months. Blood samples were collected from two pigs per treatment by humane puncture of the ear vein for haematological and biochemical analysis. In addition, two (2) gilts from each treatment were randomly selected, slaughtered and their reproductive organs excised and examined. Linear body measurements (body length, chest girth, height at withers and flank-to-flank) were also recorded. Data collected were analyzed according to factorial arrangement of treatments in a completely randomized design (CRD) whereas stepwise multiple linear regression analysis was used to generate prediction equations between body weight and linear body measurements. In experiment 2, eighteen (18) gilts with different body conditions and backfat thickness were selected and assigned to experimental treatments with six gilts per treatment. All the gilts were weighed and mated twice at the second observed estrus. Pregnancy was confirmed by the gilt not returning to heat after 21 days of observation for signs of heat after breeding. Gilts were fed 2.1 kg of an 18% CP diet daily throughout gestation. Their feed was increased to 3.0 kg of feed daily during lactation until weaning. Gilts were monitored and their reproductive indices recorded throughout gestation and lactation. The pre-weaning performances of their piglets were also recorded until weaning at day 35. Data collected were subjected to one way analysis of variance (ANOVA) for a completely randomized design (CRD). Results of the first experiment indicated that diet containing 3000kcal/kg or 3200kcal/kg metabolizable energy and 18% crude protein was the optimum required for gilts to grow faster and reach the minimum threshold of age, body weight, backfat reserve and body condition necessary for early attainment of first oestrus and future reproductive processes. On the other hand, the result also showed that when pork of a moderate fatness (lean pork) is in demand, gilts should be fed diets having 2800kcal/kg of metabolisable energy and either 16 or 18% crude protein. High coefficient of determination (R2) values of 0.96, 0.95, 0.93 and 0.45, respectively, were recorded between body (Y) weight and body length (BL), heart girth (HG), flank-to-flank (FF) and height-at-withers (HW) measurements. Prediction equations for body weight of the gilts were, Y = 0.83 x BL – 33.53, Y = 1.07 x HG – 37.86, Y = 1.22 x FF – 37.14 and Y = 0.86 x HW – 14.83. Results of the multiple linear regression showed that with effective management, farmers, researchers and prospective pig buyers can use the prediction equations for body length, heart girth and flank-to-flank measurements to easily estimate the body weight of their pigs especially, during selection, drug administration and/or determination of market weight and prices. In the second experiment, results showed that body condition of gilts at mating affected their gestation weight gain, lactation body weight losses, litter size at birth and weaning, growth rate of their piglets, pre-weaning mortality and weaning-to-estrus intervals, etc in favour of gilts with normal and fat body conditions. It was concluded that in any commercial pig industry where the management is interested in increasing sow lifetime productivity, replacement gilts should be scored for body condition both subjectively and objectively using ultrasonic equipment to determine their readiness to undergo the stress of growth and reproduction. From an economic point of view, this is an important factor that should be considered to determine the total value of pigs produced within a given cycle. Hence, it is recommended that breeding gilts should have at least between 15mm and 18mm backfat thickness at first mating for effective and more balanced reproductive processes.
TABLE OF CONTENTS
Pages
Title Page………………………………………………………………………………………….i
Certification………………………………………………………………………………………ii
Dedication………………………………………………………………………………………..iii
Acknowledgement………………………………………………………………………………..iv
Abstract…………………………………………………………………………………………..vi
Table of Contents………………………………………………………………………………..viii
List of Tables………………………………………………………………………………….…xiv
List of Figures……………………………………………………………………………………xvi
CHAPTER ONE 1
1.1 INTRODUCTION 1
1.2 OBJECTIVES OF THE STUDY 4
1.3 JUSTIFICATION 4
CHAPTER TWO 7
LITERATURE REVIEW 7
2.1 GROWTH OF PIGS 7
2.1.1 Measures of postnatal growth in pigs 7
2.1.2 Allometric growth 8
2.1.3 Nutritional influence on growth rate 8
2.1.4 Effect of temperature on growth of pigs 9
2.1.4.1 Effect of temperature on performance of pigs 10
2.1.4.2 Effect of temperature of growth rate of piglets 11
2.1.5 Physiological effect of hormones on growth 12
2.1.6 Birth weight in relation to postnatal growth of pigs 14
2.1.7 Prenatal development of muscle fibre in the pig 15
2.1.8 Growth rate of pigs relative to their birth and weaning weights……………………….15
2.2 NUTRIENT REQUIREMENTS OF PIG 16
2.2.1 Protein and amino acids requirements for growth of pigs 17
2.2.2 Energy intake of gilts and sows 18
2.2.2.1 Physiological explanation for small litter size, reduced conception rate and follicular growth 18
2.3 NUTRITION AND REPRODUCTIVE PERFORMANCE 19
2.3.1 Nutrition and ovulation rate 19
2.3.2 Nutrition and puberty 21
2.3.3 Energy restriction and length of estrus cycle 21
2.3.4 Influence of diet on follicular development 22
2.3.5 Influence of diet on embryo survival 22
2.3.6 Feed intake and weaning-to-oestrus interval 23
2.4 PHYSIOLOGICAL PATHWAY INVOLVING NUTRITION AND REPRODUCTION 24
2.4.1 Physiological role of insulin on reproduction 24
2.4.2 Nutrition and hormonal mechanisms involved in reproduction. 25
2.4.3 Physiological relationship between high feed intake and progesterone secretion 25
2.5 MANAGEMENT AND FEEDING OF GILTS DURING GESTATION 26
2.5.1 Gestational weight gain 29
2.6 FEEDING OF GILTS DURING LACTATION 30
2.6.1 Effect of lactation feed intake on weaning-to-estrus interval 31
2.6.2 Effect of lactation feed intake on ovulation rate…………….………………………….31
2.6.3 Lactation body weight loss 31
2.7 ONSET OF PUBERTY IN GILTS 32
2.7.1 Factors that influence age at onset of puberty in gilts 32
2.7.1.1 Nutritional effect on the puberty attainment in gilts 34
2.7.1.2 Impact of boar exposure on the onset of puberty 35
2.7.1.3 Effect of season on age at puberty 35
2.8 CONDITION SCORING IN PIG PRODUCTION 36
2.8.1 Body condition at breeding 38
2.8.2 Body condition at farrowing 39
2.8.3 Body condition at weaning 39
2.9 MEASURING BACKFAT 39
2.9.1 Backfat thickness and reproductive performance in sow 40
2.9.2 Backfat thickness and body lipid 41
2.10 MILK PRODUCTION OF SOW DURING LACTATION 42
2.10.1 Estimating milk production 44
2.11 SOME MEASURES OF REPRODUCTIVE PERFORMANCE IN FEMALE PIGS 45
2.11.1 Litter size 45
2.11.1.1 Some factors that determine the size of weaned litter 46
2.11.2 Number of parity 46
2.11.3 Age at weaning 46
2.11.3.1 Advantages of early weaning 49
2.11.4 Liveweight at weaning 49
2.11.5 Litter birth weight 49
2.11.6 Piglet mortality 50
2.11.7 Weaning-to-estrus interval 51
2.11.7.1 Physiological explanation for prolonged weaning-to-estrus interval 52
CHAPTER THREE 54
MATERIALS AND METHODS 54
3.1 Location and duration of study 54
3.2 Management of experimental animals 54
3.3 Experimental diets 54
3.4 Experimental design 56
3.5 Statistical design 60
CHAPTER FOUR 64
RESULTS 64
EXPERIMENT I 64
4.1 EFFECT OF DIETARY ENERGY AND PROTEIN ON THE GROWTH AND REPRODUCTIVE PERFORMANCE OF GILTS 64
4.1.1 The effect of dietary treatments on some reproductive and growth indices of gilts 64
4.1.1.1 Age at first oestrus 64
4.1.1.2 Body weight at first oestrus 65
4.1.1.3 Daily feed intake 65
4.1.1.4 Growth rate 66
4.1.1.5 Feed conversion ratio 66
4.1.1.6 Backfat thickness 67
4.1.1.7 Body condition score (BCS) 67
4.1.2 Relationship between age at first oestrus, and body weight at first oestrus, growth rate, backfat thickness and BCS 77
4.1.3 Effect of dietary energy and protein on weight of reproductive organ, weight of ovary and ovulation rate 78
4.1.3.1 Weight of reproductive organ 78
4.1.3.2 Ovarian weight 78
4.1.3.3 Number of corpus luteum (ovulation rate) 79
4.1.4 Relationship between weight of reproductive organ, ovarian weight and number of corpus luteum 82
4.2 EFFECT OF VARYING ENERGY, PROTEIN AND ENERGY X PROTEIN INTERACTION ON THE HAEMATOLOGICAL INDICES OF GILTS 84
4.2.1 Packed cell volume 84
4.2.2 Haemoglobin concentration 84
4.2.3 Red blood cell 85
4.2.4 White blood cell 85
4.2.5 Mean corpuscular volume 85
4.2.6 Mean corpuscular haemoglobin concentration 86
4.2.7 Mean corpuscular haemoglobin 86
4.2.8 Bilirubin 86
4.2.9 Aspartate transaminase or serum glutamic oxaloacetic acid (SGOT) 87
4.2.10 Alanine transaminase or serum glutamic pyruvic acid (SGPT) 87
4.2.11 Alkaline phosphatase 87
4.3 Effect of dietary energy and protein levels on linear body measurements of gilts at first oestrus 91
4.3.1.1 Body length 91
4.3.1.2 Heart girth 91
4.3.1.3 Flank-to-flank 91
4.3.1.4 Height at withers 92
4.3.2 Relationship between body weight and linear body measurements of gilts 95
EXPERIMENT II 97
4.4 Effect of body condition on the reproductive performance of gilts 97
4.4.1.1 Gestation length 97
4.4.1.2 Gestation body weight gain 97
4.4.1.3 Gestation backfat gain 97
4.4.1.4 Backfat of gilts at farrowing 97
4.4.1.5 Lactation body weight loss 98
4.4.1.6 Lactation backfat loss 98
4.4.1.7 Sow 21 day milk production 98
4.4.1.8 Weaning-to-oestrus interval 99
4.4.2 Effect of body condition of gilts on litter performance 101
4.4.2.1 Average litter size at birth 109
4.4.2.2 Average litter size at weaning 102
4.4.2.3 Average piglet birth weight 102
4.4.2.4 Average piglet weaning weight 102
4.4.2.5 Average piglet growth rate 102
4.4.2.6 Percent survival to weaning 103
4.4.2.7 Pre-weaning piglet mortality 103
CHAPTER FIVE 106
DISCUSSION 106
EXPERIMENT I 106
5.1 Effect of dietary energy and protein on the attainment of puberty in gilts 106
5.2 Effect of dietary energy and protein on haematological and biochemical indices of gilts 115
5.3 Effect of dietary energy and protein level on linear body measurements of gilts at first oestrus 116
5.3.1 Relationship between body weight and linear body measurements of gilts 117
EXPERIMENT II 118
5.4 Effect of body condition at mating on the reproductive performance of gilts and pre-weaning growth of their piglets 118
5.5 Summary and conclusion 126
REFERENCES…………………………………………………………………………………128
CHAPTER ONE
Recent report (Spore, 2007) showed that pork is the world most widely consumed meat making up about 40 per cent of the total meat consumed worldwide. The high pork consumption has been attributed to the high cost of beef and the fear of avian influenza for poultry (Spore, 2007). In Africa, however, it barely accounts for 10% of meat consumed. From 1990 to 2005, its production has risen from 500,000 to 800,600 tonnes, probably as a result of rapid urbanization which interestingly has boosted production (Spore, 2007). In Nigeria, FAO (2005) reported a 4 per cent increase in the annual growth rate for pig production from 1990 to 2000 and this was adjudged to be the highest among other livestock species.
These reports are an indication that swine production has the potential for bridging the protein deficiency gap in this country. This is because pigs are endowed with natural genetic potentials that support rapid growth and high reproductive performance. For instance, pigs have a rapid growth rate and demonstrate excellent capacity for reproduction being litter-bearing in nature (Holness, 2005). They are characterized also by the best efficiency of nutrient transformation into high quality animal protein (Spore, 2007). These attributes have not been completely harnessed in this country thus leading to the slow increase in the supply of pork.
The performance of the breeding herd is fundamental to the financial success of any pig enterprise. According to White (1996) and Whittemore (1998), pig production is often assessed based on the number of litters produced per sow per year, the number of piglets produced per litter, and the viability of those piglets. Also, the lifetime productivity of the female within the herd is taken into account. Thus, the young gilt represents the future of any pig enterprise and if not fed properly, is unlikely to achieve her reproductive potential of rearing 60 to 70 pigs over 6 to 7 parities (Scharlach, 1998). It is therefore necessary to provide gilts with adequate nutrition in order to maximize litter growth rate, and minimize empty sow-days thus increasing the size of subsequent litters. Good nutritional preparation of the gilt from selection to first farrowing is essential in achieving this goal. Soede et al. (2007) reported that good nutritional management of gilts makes them to be mature, well grown and in good body condition at service, resulting in better conception rate and litter numbers. They emphasized that far too many gilts are weaned in poor condition and do not conceive or have poor second litters leading to an inexcusable waste of breeding potential.
The types of feedstuff, environment, feeding system for pigs differ around the world, and the nature of these differences is reflected in the growth and reproductive efficiency of pigs around the world. Thus, there is variation within and between temperate and tropical breeds of pigs in age of puberty, maturity, gestation length, age and weight of pigs at weaning which are major determinants of performance (Dritz, 2004; Pluske, 2006). As a result, most pigs in the tropics hardly reach the live weight of those exposed to temperate feeding system. Therefore, it is necessary to categorize pigs in the tropics according to weight ranges obtainable in the zone.
Research reports indicate that nutrition during the rearing of the gilt may influence the length of her reproductive life (Scharlach, 2000; Close, 2003). Scharlach (2000) reported that feeding programs for gilts should be aimed at the female possessing targeted amounts of body fat, bone, and lean at critical points in time such as selection, first breeding or conception, gestation, farrowing, and at weaning. The author noted that maximum longevity is obtained by incorporating the best combination of nutritional regimes during the periods preceding each one of these events (Scharlach, 2000). Therefore, an accurate estimate of fat reserve using both subjective and objective body condition score (BCS) techniques several times during rearing provides targets at which nutritional program can be aimed (Close, 2003).
In modern pig production, nutrition and management play an important role in enhancing reproductive performance of the sow. According to Close (2003), there is need to ensure that the correct target body condition at first mating is achieved and that nutritional needs are met during gestation and lactation. The overall objective is to ensure that, as far as is possible, the sows achieve a good level of performance on all farms.
Condition scoring of pigs allows farmers to determine if their pigs are thriving in the system of management they are kept. Condition scoring is necessary in every type of pig production system as an important management practice. This also applies to other farm animals like sheep, goat, and cattle (Cobb, 2005; Singh-Knights and Knights, 2005; Taiwo et al., 2005). Body condition scoring (BCS) is an estimate of the muscle and fat development of an animal. It can be assigned to an animal either by visual appraisal, by palpation or by combining sight and touch. Animals are given a score from 1 (Emaciated) to 5 (Obese) based on the level of muscling and fat deposition around the loin. It is expected that healthy, well nourished animals should not be too fat or thin.
The body condition of the gilt at first mating has a significant effect on sow lifetime performance. Available records (Gueblez et al., 1985; Gaughan et al., 1995; Challinor et al., 1996) have suggested that animals that do not have sufficient body condition when first selected and introduced into the farm, generally fail to achieve a reasonable number of parities. The better the body condition, the better the lifetime performance of the animal. It is suggested therefore, that gilts should be sufficiently mature, of an appropriate body condition and have adequate reserves of lean and fat in her body prior to breeding. The adequate reserve of fat in her body is necessary not only to initiate the reproductive processes per se, but also to act as a buffer in times of nutritional inadequacy, when metabolic needs exceed nutrient intake (Close, 2003). Furthermore, body reserves are also needed to protect the animal in poor nutritional environmental circumstances. Close (2003) indicated that gilts should be of sufficient age, size, maturity and achieve a certain target body condition at first mating. For instance, gilts should be about 220-230 days of age; 130-140kg body weight; have 16-20mm P2 backfat thickness and mated at 2nd or 3rd oestrus (Close, 2003).
Cobb (2005) recommended that animals should be condition scored at three critical times namely: few weeks before breeding, at parturition and at weaning. During pregnancy, the objective should be to feed sow a good quality gestation diet for a specified target body weight gain and achieve a body condition score of 3.5 at parturition (scale 1-5) (Cobb, 2005). The significant need to increase feed intake during pregnancy can not be overemphasized. This is done to ensure a high rate of foetal growth, to maintain the sow in good body condition and to promote the proper development of the mammary glands, which are essential for good colostrum and subsequent milk production.
Gilts on good body condition prior to mating is expected to wean piglets of good body weight, with minimal loss of body weight and body condition of the sow. It may be pertinent to state that lactation is, perhaps, the most critical period in the life of the pig and the nutritional strategies implemented prior to and during this period, influence both the growth and development of the piglets through to slaughter, as well as the subsequent reproductive potential of the sow and overall productivity.
Most researches in Nigeria have focused on feeding pigs based on feed restriction and on percent body weight alone (Amaefule et al., 2006; Ugwu and Onyimonyi, 2009). There is a dearth of information on the application of backfat measures and body condition score as a standard in feeding pigs in the country. For this to be achieved, it is necessary to understand the best diet combination (protein and energy) that supports growth and reproductive efficiency of the sow especially at different stages in production.
The main objective of the study was to determine the reproductive performance of gilts with varying body conditions.
The specific objectives were to;
- determine the impact of varying dietary energy and protein levels on age at first oestrus of gilts.
- determine the best energy and protein diets that improve growth and body condition of gilts at first oestrus.
- develop prediction equations for estimating body weight of gilts using linear body measurements.
- determine the effect of body condition score at first mating on the reproductive performance of gilts and;
- determine the pre-weaning growth of the piglets.
According to Kirkwood et al. (1988), adequate attention should be given to replacement gilts because they constitute a significant proportion of most commercial breeding herds and therefore represent the future of any pig enterprise. However, due to management and nutritional problems, this group of pigs has been neglected and most of them are not able to meet or achieve their reproductive potential of rearing 60 to 70 pigs over 6 to 7 parities as reported by Scharlach (1998). This situation calls for concerted effort in undertaking research aimed at improving the reproductive ability of these animals via research in nutrition and management.
Good nutritional preparation of the gilt from selection to first farrowing is essential in solving the problem of low reproductive performance of pigs in the tropics because, it makes them to be well grown and in good body condition to enter their first reproductive life after puberty. Unfortunately, it is on record that far too many gilt are bred in poor condition and most time they experience difficulty at conception (Soede et al., 2007).
Although energy and protein requirements for pigs have already been developed in temperate areas, these need to be revised under tropical condition considering the effect of temperature and relative humidity on feed intake and heat dissipation. Higher ambient temperature results in lower feed intake. Therefore, diet composition needs to be revised or adjusted to provide diets with adequate balance of protein-energy ratios suitable for reproductive development of animals in the tropics (Patience, 1996). According to Patience (1996), factorial estimates of nutrient requirements are not yet sophisticated enough to describe optimum feeding programs, those strategies that define the method of feeding before and during gestation and lactation, or phases within each, to maximize overall productivity or efficiency. For example, there is now considerable activity devoted to the feeding of gilts to achieve a desired body composition/condition, much as is done in broiler breeders.
In animals, fat is the principal form of energy storage, so, the size of fat reserves has long been of interest in animal science and related fields. Animals with large fat reserves have often been termed “in good condition” and those with a low or no reserve “in poor condition”. The concept of body condition pervades so much of animal science that it becomes important for farmers and researchers to understand first, what exactly is meant by body condition, and second, how body composition can be measured to provide access to information on the size of energy reserves. A simplistic view of fat would be that it serves as a compact energy source for fueling metabolism during periods of energy shortfall; the fatter the fitter (Donald, 2002). According to Tokach and DeRouchey (2006), too little backfat reserves can reduce reproductive performance and increase sow mortality. Low backfat reserves also can be an animal welfare concern as thin sows have a greater chance of developing shoulder sores. The authors further reiterated the existence of some disagreement on whether the ideal backfat level at farrowing should range between 16-18 mm and 18-21mm, but according to Tokach and DeRouchey (2006), researchers agree that the most important point is to have as few sows as possible below 15mm or above 24mm at farrowing. Presently, there is disagreement over the best way to set feeding levels to make sure sows are not under-or over-fed in gestation. Body condition score though important, only explains about 23% of the variation in backfat levels indicating that a visual body condition score is a poor predictor of actual backfat level (Tokach and DeRouchey, 2006). This further buttresses the importance of monitoring backfat levels periodically especially during those critical period (few weeks before breeding, gestation and farrowing) using simple ultrasonic device. Records show that farmers trusted their eyes to determine how a sow would be fed. Simply, most swine producers look at the sow, and base the feeding program on that fairly-quick judgment of its body condition score (Melgores, 2003). Fortunately, backfat depth can now be assessed using a simple device, a Lean Meater. There is need to recommend a good diet combination (protein and energy) that supports the deposition of sufficient and an adequate fat reserve that places an animal in the best condition suitable for reproduction.
Because of the difficulty encountered in weighing individual sows on many farms, the study hopes to establish weight categories for pigs in the tropics that can be estimated by using linear body measurement (using girth or flank measurement).
Also, in Nigeria, available data (Taiwo et al., 2005) revealed that backfat is routinely measured at slaughter as a determinant of the carcass value. Fortunately, modern and easy to use equipment for measuring backfat in pigs is now available. In live animals, backfat depth can be assessed using a lean-Meater. It has been reported that results of backfat thickness taken using the equipment correlates highly with backfat measurements at slaughter (Chiba, 1995). The site of measurements is generally at the 10th rib, two to three cm lateral to the midline.
According to Moeller (2002), the relatively low investment cost and perceived ease of operation, made them widely used for seed stock selection, central testing programs, university and industry research as well as on-farm application. Still today, many swine producers and researchers continue to utilize this technology for measuring backfat depth due to the low investment cost. However, this has not been widely explored in Nigeria.
According to Scharlach (1998), Melgores (2003) and Tokach and DeRouchey (2006) research attention has focused on the importance of deposition and maintenance of body fat reserves. Low body fat reserves are still a major problem on many commercial pig farms. Some sows appear to be in a good condition but are marginal in fat reserves (Scharlach, 1998). It is unfortunate that these important considerations in pig reproduction are not given much attention in the tropics.
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