Predicting growth rates of adult working boars in a commercial Predicting growth rates of adult working boars in a commercial boar stud boar stud

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Introduction
Weight gain is inevitable in breeding boars because they enter the boar stud at a young age and light weight.It is typical for working boars to start their reproductive life between 300 and 350 lb, and gain more than 250 lb throughout their lifetime.The relationship between growth rate and reproductive performance of breeding boars may be important.In previous studies, slow-growing boars fed at maintenance have shown significantly decreased libido, semen volume, and sperm output.On the other hand, fast-growing boars fed at high rates are thought to have increased leg and libido problems.Rate of weight gain may also have an impact on longevity, and thus affect lifetime semen production.But the ideal growth rate for adult working boars remains unclear.This lack of information on growth rates of adult boars during their lifetime is a major challenge, but estimates can be made if the relationship between body weight and age of the boar is known.Moreover, predicting growth rates can be very helpful in developing 1 Zoltenko Farms, Inc., Hardy, NE 68943.

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Food Animal Health and Management Center, College of Veterinary Medicine.appropriate feeding programs that can be used to set different growth curves.Therefore, this study aimed to predict growth rates in adult working boars in a commercial boar stud.

Procedures
A total of 214 adult working boars from two genetic lines Franklin,KY) were used in this study.Boars were selected to obtain the widest possible range in age and weights.Boars were individually weighed on a platform scale, and age of the boar was recorded at the same time.Boars were fed and housed in a commercial boar stud according to standard procedures of the farm.Diets were not manipulated for this study.All boars were fed a corn-soybean meal diet with 10% soy hulls and 5% dehydrated alfalfa, formulated to meet or exceed suggested lysine and energy requirements.
A regression equation to predict boar weight by using age of the boar was developed by using PROC REG of SAS.This model was used to predict BW for a specific age on a daily basis.Then, ADG was derived as the difference between consecutive predicted BW values.The ADG for a specific weight range is computed by taking the average of the predicted ADG of the lowest and highest value of the weight range desired.
Daily ME requirement (Mcal ME/d) and feeding rates (lb/d) under thermoneutral conditions were estimated by using the factorial approach.Requirements for maintenance, weight gain, mating activity, and sperm production were individually determined by using regression equations, and were added to estimate total daily ME requirement.The energy requirement for weight gain was determined by using the predicted ADG as a guide in setting target weight gains.The accuracy of feed drops in the facility was previously tested, and an average of 12% overage from the desired feed setting was determined.This was then used to adjust the feed box setting to obtain the desired feed allocation for each weight range.Finally, a phase-feeding program for adult working boars was developed from the estimates for daily ME requirement.

Results and Discussion
The modeled live-weight curve in boars as a function of age exhibited a positive curvilinear response (P<0.01; Figure 1).The model was: The predicted BW increased from 330 to 642 lb from an age of 220 to 620 d; that is an 80 lb increase for every 100 d.But the increase in BW decreased dramatically to a total of 50 lb from 620 to 1000 d of age.The developed equation was used to derive ADG from the predicted BW, and showed a negative curvilinear response as the boars aged (Figure 2).Predicted ADG decreased from 1.24 lb/d at 350 lb to 0.12 lb/d at 700 lb (Table 1).There are very few studies evaluating boar growth, but scientists from the Netherlands combined experimental and field data, and suggested a growth rate of 1.10, 0.88, 0.66, 0.44, 0.22, and 0.11 lb/d for boars weighing 330, 440, 550, 660, 770, and 880 lb, respectively.In this study, predicted ADG was 23, 20, and 6% higher than the Dutch recommendations at 330, 440, and 550 lb, respectively (Table 2).At 660 lb, the predicted ADG was 50% less than the Dutch recommendations.There may be a number of reasons that can explain the differences in growth rates, such as genetic, dietary, environmental, and even procedural differences, but the predicted ADG in this study is similar to the Dutch recommendations.This may indicate that relating BW and age of an appropriate sample of boars from a given farm population can be a practical method in predicting on-farm growth rates.This agrees with previous research at Kansas State University in finishing pigs, in which real-time ultrasound scans of backfat and longissimus muscle area across different age groups of pigs were used effectively to determine daily protein and lipid accretion rates.Therefore, the data-collection method described herein can be employed to either determine farm-specific nutrient requirements or to develop appropriate feeding programs.
As an example, a phase-feeding program for adult working boars was developed from the predicted growth rates in this study.Facto-rial estimates of daily ME requirement and feeding rate were made for adult working boars from 300 to 700 lb (Table 3 6.5, and 6.7 lb/d at 300 to 400, 400 to 500, 500 to 600, and 600 to 700 lb, respectively.This feed allocation provided 8.2, 8.4, 8.7, and 9.0 Mcal ME/d.These represented the four phases of the proposed feeding program.The daily ME intake of boars in the phase-feeding program fitted well with their daily ME requirement (Figure 3).Finally, the feed allocation was adjusted according to the accuracy of feed drops in the farm.An average of 12% overage from the desired feed setting was determined, and this was accounted for in the final feed allocation.The proposed phasefeeding program in boars, with the appropriate adjustments in feed allocation, is shown in Table 4.
In conclusion, relating age and body weights of boars in a given farm population can be an efficient and accurate method to model on-farm growth and predict growth rates.These data can then be used to develop farm-specific feeding programs or to set different growth curves for experimental purposes.

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Figure 2. Predicted ADG of Adult Working Boars from 220 to 1000 d of Age.

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Figure 1.Relationship of Boar Age and Body Weight (214 boars).
3 Figure 3. Relationship of Daily ME Intake (Mcal ME/d) and ME Requirement (Mcal ME/d) in Adult Working Boars under a Phase-feeding Program.