FEED EFFICIENCY IN SWINE. I. A COMPARISON OF MEASUREMENT PERIODS AND METHODS OF EXPRESSING FEED EFFICIENCY 1

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1 T FEED EFFICIENCY IN SWINE. I. A COMPARISON OF MEASUREMENT PERIODS AND METHODS OF EXPRESSING FEED EFFICIENCY 1 O. W. Robison and ]. M. Berruecos 2 North Carolina State University, Raleigh Summary HE objective of this study was to evaluate different methods of measuring feed efficiency. The data were collected from 321 individually fed barrows, representing 62 sires. Gain and feed consumption were measured during age (76 days) to weight (93.5 kg) (AW), weight (45.5 kg) to weight (93.5 kg) (WW) and age (83 days) to age (130 days) (AA) periods. Feed/gain (), gain/feed () and average daily gain (ADG) were evaluated for the three periods. Heritability estimates for in AA, WW and AW intervals ( and , respectively) were higher than those for in the same intervals (0.00, 0.08 and 0.55, respectively). Further, the coefficients of variation were much smaller for in the AA and WW periods. For the AW interval, the coefficient of variation for was similar to that for. Thus, the smaller values of the coefficient of variation and the larger estimates of heritability indicate that is a more satisfactory measure of efficiency. In comparing the intervals, the WW period had a slightly higher heritability and coeff of variation than the AW period. Thus, there appears to be little difference in the two periods. Corrections for maturity and/or maintenance during AA, WW and AW intervals decreased the heritability estimates of and. Therefore, it does not appear that corrections for maturity and/or maintenance are necessary. However, correction for live backfat at 93.5 kg resulted in a small increase in the heritabilities, suggesting that efficiency of lean meat production may be slightly more heritable than gross efficiency. t Paper No of the Journal Series of the North Carolina State University Agricultural Experiment Station, Raleigh. Present address: Institute Nacional de Investigaciones Pecuarias, S.A.G., Kin Cart. M6xlco-Toluca, M6xico 10, D.F. 643 Introduction Efficiency of feed utilization is perhaps the most important trait affecting the economics of swine production. Approximately 75 to 80% of the total cost of raising swine is attributable to feed cost. To evaluate feed efficiency it is necessary to realize that it is a ratio between two direct measurements, gain (G) and feed (F). It is clear that the interpretation of results depends on which ratio, or, is used as a measure of feed efficiency. Titus, Mehring and Brumbaugh (1953) refer to as "feed conversion" while Sutherland (1965) and Falconer (1960) call it "efficiency of feed use" and "inefficiency", respectively. Further, Titus et al. (I 953) use "feed efficiency" for, whereas, Magee (1962) prefers "desirable feed efficiency" for. Timon and Eisen (1970) compared the ratios and for constant weight and constant age intervals in mice. They concluded that should be used. Nordskog, Cornstock and Winters (1944) suggested that a standard age period was better than a standard weight period for evaluating efficiency in swine. Some workers have suggested a need for correcting "feed efficiency" for maintenance requirements (Rahnefeld et al., 1965; Koch et al., 1963). Apparently correction for body composition has not been attempted. It is evident that further efforts are needed to ascertain appropriate measurement periods and methods for expressing feed efficiency in swine. The objectives of this study were to compare the ratios and as expressions of feed efficiency, to evaluate possible corrections for maintenance or body composition and to explore age to age, weight to weight and age to weight periods for evaluating feed efficiency in swine. JOURNAL OF ANIMAL SCIENCE, vol. 37, no. 3, 1973

2 644 ROBISON AND Materials and Methods This study was conducted during 1967 to 1969 at the North Carolina Agricultural Experiment Station, Raleigh. Data were collected on 321 barrows, 112 Duroc and 209 Yorkshire, representing 62 sires and 164 litters. All pigs were weighed at the start of the feeding test (65 days) and at 14-day intervals until they reached slaughter weight (93.5 kg). Feed consumed during each 14-day period was recorded. All pigs were maintained in individual solid floor pens (1.22 x 4.27 m) and selffed a pelleted corn-soybean meal ration containing 16% protein. Average daily gain (ADG), feed consumed/ gain () and gain/feed consumed () were calculated from constant age (76 days) to constant weight (93.5 kg), from constant weight (45.5 kg) to constant weight (93.5 kg) and from constant age (83 days) to constant age ( 130 days). Linear interpolations between weekly measures of feed consumed and ADG were used in order to obtain "constant" ages and weights, except for slaughter weight. Lifetime average daily gain (ADGL) was included as a trait also. At 93.5 kg live weight, back/at thickness was evaluated using the method of Hazel and Kline (1952). Measurements were made at the seventh rib and at the mid-loin about 2.5 cm off the mid-line. Animals were weighed off test weekly, were slaughtered at approximately 93.5 kg and carcass data were obtained approximately 24 hr. after slaughter. The least squares modei for all analyses was as follows: YlJkl---/*-'t-YSBi-~-Sj~i)-~-DktD-~-EiJkl, where was the fitted mean; YSBt was the effect of the i th year-season-breed; Sj,~ represented the effect of the jth sire nested in the i th YSB; Dklj) was the k th dam nested in the jth sire and e~ju~ was the random error. Genetic variances and covariances were calculated from the sire components of variance and covariance (Dickerson, 1960). Standard errors of the heritability estimates were computed using the method of Osborne and Patterson (1952). Tallis's (1959) procedure was used to compute standard errors of genetic correlations. When evaluating adjustment procedures, the data were adjusted by adding the appropriate factors as covariates to the above model. In order to evaluate which ratio ( or ) should be used as an estimate of feed BERRUECOS utilization, a comparison between the two was made for three intervals, viz., age to weight (AW), age to age (AA) and weight to weight (WW) constant intervals. The comparison was made using the phenotypic and within litter coefficients of variability (Timon and Eisen, 1970) and the heritability for each trait in each interval. It was also of interest to compare the three intervals. Since the ratios ( and ) and the intervals (AA, WW and AW) may be affected by maintenance and/or maturity, adjusted values for and were obtained as follows: (1) in the age to age interval, by average weight and at mid-test and by starting weight; (2) for the weight to weight interval, by average age at mid-test, by days on test and by days on test and starting age; and, (3) in the age to weight interval, by starting weight and days on test and by days on test. Efficiency of feed utilization may be divided into efficiency of tissue formation and an efficiency in other metabolic processes such as maintenance. In order to evaluate the importance of maintenance and other metabolic processes in efficiency,, and ADG for the AW interval were corrected for percent lean cuts and/or live backfat probe. These adjustments should correct for the underestimation of efficiency of fatter animals (Timon and Eisen, 1970). After these corrections, comparisons were made using procedures similar to those in the comparison of non-adjusted measurements. Results The numbers of sires and offspring for each year-breed-season subclass are shown in table 1. Means of weights, ages and feed consumed, by intervals, are given in table 2. The test intervals were computed from approximately 76 days to 93.5 kg for the age to weight constant (AW), from approximately 45.5 kg to 93.5 kg for the weight to weight constant (WW) and from approximately 83 to 130 days for the age to age constant (AA) intervals. The longest interval was for the AW and the shortest was for the AA interval. Furthermore, AW includes both WW and AA. The intervals WW and AA overlap in the weight range from 45.5 to 72.7 kg of live weight. Comparison o] Feed Consumed~Gain and Gain/Feed Consumed Ratios. Intralitter and phenotypic coefficients of variation were calculated for feed consumed, gain, and

3 FEED EFFICIENCY IN SWINE 645 TABLE 1. NUMBER OF SIRES AND OFFSPRING BY YEAR, SEASON AND BREED Year and season of birth B reed Fall" Spring Fall Spring Fall Spring Total Duroc 3 (14) 3 (11) 5 (21) 5 (24) 5 (29) 3 (13) 14 (1t2) Yorkshire 8 (44) 8 (47) 4 (27) 6 (25) 5 (30) 7 (36) 38 (209) Total 11 (58) 11 (58) 9 (48) 11 (49) 10 (59) 10 (49) 62 (321) a Numbers of offspring in parentheses. for the three intervals. Coefficients of variation and heritabilities for these traits are presented in table 3. The heritabilities for feed consumed (0.37, 0.19 and 0.00) were low and in agreement with those reported by Park (1965) (0.29, 0.16). Sutherland (1965) reported 16 estimates with an arithmetic average of 0.16, for the heritability of feed consumed in mice. Heritabilities for ADG in all intervals were higher, in general, than those reported in the literature. The heritability of ADG tended to increase as the time on test increased; i.e., larger in AW and smaller in AA. However, the value for the heritability of ADGL was much smaller. This indicates that inclusion of the pre-test information (from birth to 28.6 kg) reduced the size of the heritaiblity relative to that obtained from the test information. An effect like this is expected where the heritability of ADG during the pre-test period is smaller than the one for ADG during the test period. A negative genetic covariance between direct and maternal effects, as reported by Ahlschwede and Robison (1971), would result in a decreased heritability during the pre-test period. Baker, Hazel and Reinmiller (1943) found that the heritability for gain during the first periods of life were small (0.07 and 0.15 for periods from birth to 21 days and from 21 to 56 days, respectively). They attributed this effect to the large variation between litters. Further, they have shown that he.ritabilities at TABLE 2. MEANS OF THE TRAITS FOR THE THREE FEEDING INTERVALS Interval Age Wt Age Trait to age to wt to wt Feed consumed/day (kg) Avg daily gain (kg) , Feed consumed/gain ,40 Gain/feed consumed Mid age (da) Mid weight (kg) Days in interval later ages are larger than those at earlier ages. Blunn, Baker and Hanson (1953) reported a value of 0.02 for the heritability of gain from birth to 56 days. The heritabilities of correspond to the higher portion of the range given by Craft (1958) for this trait (0.08 to 0.72). Johansson and Rendel (1968) and Pirchner (1969) have indicated that higher values of heritabilities for and ADG can be expected when the pigs are individually fed. The heritability values for were smaller than those reported in the literature with the exception of the value for the AW interval. When comparisons are made between the values found for and in the same period of time, the heritabilities were always higher for the ratio. Considerably smaller values were found for the coefficients of variation in with the exception of the AW interval, where the values were similar. It should be noted that, although the ratios and are computed from the same values, there is a marked curvilinear relation between the two expressions of efficiency. Further, it is evident from these analyses that the use of, rather than, results in more distinct differences among groups, i.e., half-sibs. On the basis of these results, seems to provide a better estimate of efficiency than for the AA and WW intervals with no advantage for either ratio in the AW interval. Comparisons between AA, WW and AW for measuring ADG seem to indicate that there is no difference between WW and AW but both are slightly superior to AA. These results differ from the findings of Nordskog et al. (1944) and Biswas et al. (1966). Both reports indicated no advantage in WW, compared with AA, for measuring ADG. However, in the present study, AA occurred earlier and was a shorter interval than WW. Based on the heritability values of, WW had a slight advantage over the other two intervals. However, this difference was not statistically significant. For, very

4 646 ROBISON AND BERRUECOS TABLE 3. MEANS, COEFFICIENTS OF VARIATION AND HERITABILITIES FOR FEED CONSUMED, ADG, AND IN THE THREE INTERVALS Coefficient of variation a Trait Interval Mean Within Phenotypic h2~se Feed consumed (kg) AW WW AW Avg daily gain (kg) AA WW AW Lifetime 0. $ AA WW AW AA WW AW b a Within C.V.:within litter SD /X Phenotypic C.V.:~/a~e+a2d + or-% 0.37"4-.38 b " "4-.25 b x b Negative sire component. small heritabilities were found in the AA and in the WW intervals, suggesting that AW should be used when measuring this trait. Further, the coefficients of variability for both and were markedly reduced for the AW interval. Thus, for, no appreciable advantage was found for either WW or AW but both were superior to AA. However, when evaluating, the AW interval would be recommended. Considering the similarity of the intervals WW and AW for measuring, it may be that AW has the advantage of being more practical; i.e., it is easier to start the test at a constant age (requiring only one weighing when starting the test) whereas, pigs are usually slaughtered on a constant weight basis. Adjustments o] Efficiency ]or Maturity, Maintenance and Tissue Composition. Maturity and maintenance have been suggested as factors affecting the evaluation of efficiency (Rahnefeld et al., 1965; Koch et al., 1963). Thus, these data were adjusted, as previously outlined, in an attempt to correct for maturity and maintenance. Preliminary analyses showed nonsignificance for the regressions when only starting age was included in the models for the WW interval and when only starting weight was included in the models for the AW interval. For that reason, these were not included in further analyses. Coefficients of variation and heritabilities for the adjusted efficiencies are shown in table 4. The unadjusted values are given to facili- tate comparisons. Heritability estimates for were always larger than the corresponding values for in all intervals and for all adjustments. Coefficients of variability were considerably smaller for in comparison with during AA and WW intervals. For the AW interval there was little difference between them. These results are similar to those found earlier when no adjustments were made and support the recommendation for the use of as a measure of efficiency. In the AA interval, a considerable decrease in the heritability of was found when adjustments were made for midweight or starting weight. In the WW interval, the reduction in the value of the heritability was greater when adjustments were made for midage than for a combination of starting age and days on test or for days on test alone. In the AW interval, the reduction in heritability due to the adjustment of days on test was small (as in WW) but, a considerable reduction was found with the adjustment for starting weight and days on test. Adjustments using midweight or starting weight in the AA interval account, to a similar extent, for the differences in the effect of maintenance on. Also they account for some differences in maturity. The similarity of the heritability estimates when these two adjustments were made suggests that the differences between them are not very important. If starting weight and midweight correct only for maturity and maintenance and given the

5 Interval AA WW AW FEED EFFICIENCY IN SWINE TABLE 4. COEFFICIENTS OF VARIATION AND HERITABILITY ESTIMATES FOR ADJUSTED AND UNADJUSTED AND RATIOS Variable a See table 3 for definition. b Negative sire component. Coefficient of variation" Adjustment Within Phenotypic h2 se "+'. 28 Midwt Starting wt O b, Midwt Starting wt Midage Start. age and da on test Days on test "+' Midage Start. age and da on test Days on test :~ "q-.25 Days on test ~.26 Start. wt and da on test "~-. 26 Days on test Start. wt and da on test reduction in the sire component of variance in the adjusted efficiencies, it may be that maintenance and maturity are components in the genetic difference of efficiency. However, it may be that these two weights adjust not only for maintenance and maturity but also for some factors associated with efficiency. In this case, other interpretations need to be given with respect to the importance of maintenance and maturity. In the WW interval, the adjustments for days on test and for starting age and days on test tend to indicate that maintenance differences have a small effect on the differences between sire groups in. The adjustment for midage should remove differences due to maturity and also some of the differences in growth rate and consequently efficiency. The latter effect appears to be the most probable explanation for the considerable reduction in the heritability estimate when adjustment for midage was made. The effect of adjustment for days on test in the AW interval is similar to that in the WW interval. However, the adjustment including starting weight and days on test caused a considerable decrease in the size of the heritabilities. It is interesting to note that wherever weight was included as an adjustment factor, large reductions were found in the size of the heritabilities. This effect can be explained by considering that weights account not only for differences in maintenance and maturity but also for differences in growth rate. These weights have large sire components of variance and a high degree of genetic association with gain and efficiency..therefore, when using weights to adjust for maintenance and/ or maturity, some genetic differences for gain and efficiency were removed also. No conclusion can be drawn with respect to the importance of one effect or the other. However, considering that the adjustment for days on test in WW interval (and in AW also) gave the most accurate adjustment for ~naintenance; i.e., assuming linear increase of maintenance requirements, it can be postulated that the reduction shown when weights were used as adjustment factors were due more to direct effect of weight on gain and efficiency than for the adjustment for maintenance. Similarly, considering starting age as the closest adjustment for maturity, adjustments for weights seem to remove a much larger proportion of the sire component than that expected just for maturity itself. Furthermore, if starting age includes not only maturity, but also some other factors (which is probably more realistic), it can be suggested that maturity is not an important factor in the genetic evaluation of ratio.

6 648 ROBISON AND BERRUECOS The results found by Rahnefeld et al. (1965) were different in that the heritability of was increased (0.14 to 0.27) when they adjusted for average weight at midtest in mice. However, the authors state that these estimates are biased upward. Also, by examining the standard errors of the additive genetic variance, the difference due to adjustment seems to be nonsignificant. Corrections of, and ADG in the AW period for percent lean cuts (PLC) and live backfat probe (BF) were made in an attempt to remove differences due to tissue composition of the animals. The results of these analyses are shown in table 5. The similarity between the values from the PLC adjusted and unadjusted data tends to indicate that differences in tissue composition, as measured by PLC, did not affect the sire component of variance for, or ADG. Timon and Eisen (1970) have suggested the possibility of bias when no correction is made for tissue composition. These data indicate that either the bias is too small to be detected or that PLC is not a good measure Of tissue composition. In the present study, the heritability estimate of PLC was small (0.10) and lower than the values reported in the literature. Further, the phenotypic correlation between PLC and other tissue composition measures were small (ether extract, r=0.05; marbling, r--0.08). Therefore, it appears that, at least with respect to these data, PLC was not an adequate measure of tissue composition. Adjustment for BF yielded a nonsignificant increase in the heritabilities for efficiency (, ) as well as for gain (ADG). It should be noted that no other adjustment increased the estimate of the heritability over that of the unadjusted trait. This suggests TABLE 5. COEFFICIENTS OF VARIATION AND HERITABILITY ESTIMATES FOR, AND ADG (AW INTERVAL) ADJUSTED FOR PERCENT LEAN CUTS (PLC) AND LIVE BACKFAT PROBE (BF) Coefficient of variation a Pheno- Trait Within typic h2+se Unadjusted: ADG Adjusted for PLC: I ADG Adjusted for BF: ADG I a See table 3 for definition. TABLE 6. HERITABILITY" ESTIMATES AND STANDARD ERRORS OF, AND ADG (AW INTERVAL) UNADJUSTED AND ADJUSTED ACCORDING TO KOCH ET AL. (1963) Unadjusted Adjusted Trait h2+se Trait h2-----se 0.61~ Feed adj. to gain O Gain adj. to feed adj ADG that efficiency corrected for tissue composition may be more heritable than gross efficiency. However, it is not known if the small increment is due only to random variation or is a real increment hidden by the high values for heritabflities of the unadjusted traits. Koch et al. (1963) suggested three other methods for measuring feed efficiency--(1) average daily gain adjusted for adjusted feed consumed (adjusted for midweight), (2) average daily feed consumption adjusted for daily gain and midweight and (3) the ratio of gain/ feed consumed, with feed consumed adjusted to midweight. In order to evaluate these methods, appropriate adjustments were made in the present data. Heritabilities of these new variables are shown in table 6, along with the uncorrected values for comparison. Although the heritabilities of the adjusted values were generally lower, there were no significant differences between the adjusted and unadjusted values. Similar results were found by Biswas et al. (1966). Further, the present results are compatible with the suggestions by Sutherland (1965) of using the unadjusted ratio of as a valid estimate of efficiency. However, gain adjusted for feed consumed appears to be the equal of as an estimator of efficiency. In summary, none of the adjustments for maturity and/or maintenance increased the heritability estimates of or. Therefore, it does not appear that any adjustments for maturity and/or maintenance are needed. On the other hand, small increases in the heritability estimates were found when a correction was applied for live backfat probe at 93.5 kg, suggesting that efficiency of lean meat production may be slightly more heritable than gross efficiency. Literature Cited Ahlschwede, W. T. and O. W. Robison Prenatal and postnatal influences on growth and backfat in swine. J. Anim. Sci. 32:10.

7 FEED EFFICIENCY IN SWINE 649 Baker, M. L., L. N. Hazel and C. F. Reinmiller The relative importance of heredity and environment in the growth of pigs of different ages. J. Anim. Sci. 2:3. Biswas, D. K., P. V. Hurt, A. B. Chapman, N. L. First and H. L. Self Feed efficiency and carcass desirability in swine J. Anim Sci. 25:342. Blunn, C. T., G. N. Baker and L. E. Hanson Heritability of gain in different growth periods in swine. J. Anim. Sci. 12:39. Craft, W. A Fifty years of progress in swine breeding. J. Anim. Sci. 17:960. Dickerson, G. E Techniques for research in quantitative animal genetics, p Techniques and Procedures in Animal Production Research. Monograph. American Society of Animal Science. Q Corporation, Albany, New York. Falconer, D. S Introduction to Quantitative Genetics. The Ronald Press Co., New York. Hazel, L. N. and E. A. Kline Mechanical measurement of fatness and value of live hogs. J. Anita. Sci. 11:313. Johansson, I. and J. Rendel Genetics and Animal Breeding. W. H. Freeman and Co., San Francisco, California. Koch, R. M., L. A. Swiger, D. Chambers and K. E. Gregory Efficiency of feed use in beef cattle. J. Anim. Sci. 22:486. Magee, W. T Relationship between daily feed consumption and efficiency. J. Anim. Sci. 21:880. Nordskog, A. W., R. E. Comstock and L. M. Winters Hereditary and environmental factors affecting growth rate in swine. J. Anita. Sci. 3:257. Osborne, K. and W. S. B. Patterson On the sampling variance of heritability estimates derived from variance analyses. Proc. Roy. Soc. Edinb. 64: 456. Park, Y. I Age-constant feed efficiency of pigs. J. Anita. Sci. 24:819. Pirchner, F Population Genetics in Animal Breeding. W. H. Freeman and Co., San Francisco, California. Rahnefeld, G. W., R. E. Comstock, W. J. Boylan and M. Singh Genetic correlation between growth rate and feed per unit of gain in mice. J. Anim. Sci. 24:1061. Sutherland, T. M The correlation between feed efficiency and rate of gain, a ratio and its denominator. Biometrics 21 : 739. Tallis, G. M Sampling errors of genetic correlation coefficients calculated from analysis of variance and covariance. Australian J. Stat. 1:35. Timon, V. M. and E. J. Eisen Comparisons of ad libitum and restricted feeding of mice selected and unseletced for postweaning gain. 1. Growth, feed consumption and feed efficiency. Genetics 64: 41. Titus, H. W., A. L. Mehring and J. H. Brumbaugh Variation of feed conversion. Poul. Sci. 32: 1074.