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
LIST OF TABLES
Tables Page
Table 1: Nutrient requirement of pigs as reported by different authors 17
Table 2: The influence of premating feed intake on subsequent litter size and piglet performance 21
Table 3: Recommended feeding levels of sow/gilt during various stages of gestation 29
Table 4: Average age at onset of puberty of gilts as reported by various authors 33
Table 5: Relationship between body condition score and backfat thickness 38
Table 6: Relationship between backfat body condition and feeding intake 38
Table 7: The effect of litter size on milk yield in the sow 44
Table 8: Estimation of milk production (M), milk dry matter (DML), Energy (EL) and Nitrogen (NL) output of gilts during a 21day lactation 45
Table 9: Weaning ages of piglets as reported by various authors in different countries 48
Table 10: Percentage composition of experimental diets…………………………………………55
Table 11: Proximate composition of experimental diets…………..………………………………56
Table 12: Relationship between body condition score and ultrasonic backfat levels 57
Table 13: Pre-mating body condition score and backfat groups 59
Table 14: Percentage composition of diet used during gestation and lactation 59
Table 15: Proximate Composition of Gestation and Lactation Diets………………………………………59
Table 16: Analysis of variance of energy and protein effects on age at first oestrus, weight at oestrus, growth rate, backfat reserve and body condition score (BCS) 68
Table 17: Least square means (±SE) of the effects of energy and protein interaction on age at first oestrus, BW at first oestrus, growth rate, backfat reserves and body condition score 69
Table 18: Pearson correlation coefficients between age and body weight at first oestrus, growth rate, backfat thickness and body condition score 78
Table 19: Analysis of variance of energy and protein effects on weight of reproductive organs, and number of corpora lutea. 80
Table 20: Least square means (±SE) of the effects dietary treatments on weight of reproductive organ, ovarian weight and number of corpora lutea of gilts at first oestrus…………………………………………………………………………………………………………..81
Table 21: Pearson correlation coefficient between weight of reproductive organ, ovarian weight and number of corpora lutea 83
Table 22: Analysis of variance of energy, protein and energy x protein interaction on the haematological indices of gilts 89
Table 23: Least square means (±SE) of the effect of dietary treatments (energy and protein) on the haematological indices of gilts 90
Table 24: The analysis of variance of energy and protein effects on linear body measurements of gilts at first oestrus 93
Table 25: Least square means ± SE of the effects of energy and protein interaction on linear body measurements of gilts at first oestrus 94
Table 26: Correlation coefficients showing interrelationships between various measurements and body weight (kg) 96
Table 27: Relationship between live weights and linear measurements of pigs 96
Table 28: Stepwise multiple regression prediction of body weight from body measurements; regression coefficients. 96
Table 29: Analysis of variance and descriptive statistics of the effect body condition on reproductive performance of sow 100
Table 30: Effect of Duncan mean on the reproductive performance of sows with different body condition 101
Table 31: Analysis of variance of the effect of body condition on litter performance 104
Table 32: Effect of Duncan mean on the litter performance of gilts with different body condition 105
LIST OF FIGURES
Figures Page
Fig. 1: Interaction of energy and protein on average age at first oestrus of gilts 70
Fig. 2: Interaction of energy and protein on average body weight of gilt at first oestrus 71
Fig. 3: Interaction effect of energy and protein on average daily feed intake 72
Fig. 4: Interaction of energy and protein on average growth rate of gilts at first oestrus 73
Fig. 5: Interaction of energy and protein on average feed conversion ratio of gilts at first oestrus 74
Fig. 6: Interaction of energy and protein on average backfat thickness of gilts at first oestrus 75
Fig. 7: Interaction of energy and protein on average body condition score of gilts at first oestrus 76
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.