INFLUENCE OF NUTRITION AND BODY CONDITION AT FIRSTMATING ON THE REPRODUCTIVE PERFORMANCE OF GILTS IN THE HUMID TROPICS

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.

1.1       Introduction

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.

1.2      Objectives of the study

The main objective of the study was to determine the reproductive performance  of gilts with varying body conditions.

The specific objectives were to;

(i)              determine the impact of varying dietary energy and protein levels on age  at first oestrus of gilts.

(ii)            determine  the best energy and protein diets that improve  growth and  body condition of gilts at first oestrus.

(iii)           develop prediction equations for estimating body weight of gilts using linear body measurements.

(iv)            determine the effect of body condition score at first mating on the reproductive performance of gilts and;

(v)             determine the pre-weaning growth of the piglets.

1.2       Justification

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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