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Thyroid activity in relation to feed intake, growth rate and feed conversion in growing heifers
DOMESTIC ANIMAL ENDOCRINOLOGY
Vol, 4(3):201-206, 1987
THYROID ACTIVITY IN RELATION TO FEED INTAKE, GROWTH RATE AND FEED CONVERSION IN GROWING HEIFERS Nils Standal, Borghild Tveit and Morten Svendsen Agricultural University of Norway Department of Animal Science Box 25, 1432 As-NLH Received June 2, 1986
ABSTRACT Phenotypic and genetic parameters for thyroid activity (T~ serum level, T4 apparent distribution volume, T4 fractional turnover rate and T4 degradation), and for certain production traits (roughage dry matter intake, daily weight gain and roughage dry matter/kg weight gain), were investigated in cattle. In the experiment, 480 growing heifers were studied, daughters of 20 AI sires previously tested for thyroid activity. Repeatabilities for thyroid traits 2-3 months apart varied, with an average 0.3-0.6 for the different traits. Heritability estimates based on sire components were 0.1-0.4 for the thyroid traits, 0.16 +. 10 for roughage intake and 0.18 _. 11 for daily gain. The sire component for feed efficiency (roughage dry matter/kg weight gain) was 0, and genetic correlations between thyroid traits and the production traits in growing heifers were low with large standard errors. INTRODUCTION Thyroid activity has been one of the biological features studied in the search for physiological/endocrinological criteria to aid selection for production traits in cattle. The thyroid hormones are known to be important for milk production and are also vital for normal growth and development. Conflicting results have been reported in the literature about the relationship between different thyroid activity parameters and growth rate. Fabry (1) found a highly significant positive correlation (0.79) between daily live weight gain in a 12-month period and the serum thyroxine (T4) level at 15 to 20 days of age. In a trial under farm conditions, the same author (1) found highly significant negative correlations between T4 levels and daily weight gain during a similar period. Bobek et al (2) reported positive correlations between body weight gain from 28 to 104 days of age and T3 (0,484) and 1"4 (0,175) serum levels. Several reports have been published concerning the connection between thyroid activity and milk production traits. Joakimsen et al (3) suggested that T4 degradation might be a useful index of thyroid activity, and found a genetic correlation of 0.42 between this index in sires and fat-corrected milk yield in their daughters. In a later paper, Joakimsen (4) confirmed that there was also a positive genetic correlation when thyroxine degradation was measured on young bulls of 4-12 months of age. Similar results were reported by Sorensen et al (5). Joakimsen (4) did, however, express a need for caution in using T4 degradation as an index for pre-selection of bulls, drawing attention to the profound effect of the thyroid hormones on energy metabolism and the effect that selection for thyroid activity might have in increasing maintenance requirements. The purpose of this experiment was to study genetic and phenotypic variation and covariation in thyroid activity parameters and production traits in dairy Copyright O 1987 by DOMENDO,INC.
201
0739-7240/87/$3.00
202
STANDAL, TVEIT AND SVENDSEN
cattle. The production traits measured were daily weight gain, feed conversion and daily a d lib roughage dry matter intake in the period from 12 to 15 months of age. MATERIALS A N D METHODS
The 20 AI bulls used as sires in the experiment all had an above-average predicted breeding value for milk production based on progeny tests. All had been tested for thyroid activity twice between the ages of 4 and 12 months (4), ten had a higher T4 degradation rate than average, the remaining 10 a lower degradation rate than average. Each year from 1977 to 1985 inclusive (years 1 to 8), 3-4 daughters of each bull (about 70 heifers per year) were chosen as the experimental animals. Altogether 480 heifers com pl e t e d the experiment. They entered the experiment at 9-12 months of age in September each year and were stall-fed for 9 months, after which they were let out on pasture before continuing the experiment during their first lactation. Growth rate calculations were based on monthly weighings of the animals. Individual feed recording was performed 4 days each week for 12-16 weeks in the period from October to January. During that time the animals were individually fed grass silage twice a day. The amounts fed and recorded were intended to be a d lib. The silage not consumed was removed and recorded every second day. It proved necessary to offer in addition an ammonia-treated barley straw from January until the end of the indoor season in order to make the grass silage last, though this could not be recorded with the same precision. No feed recording was performed during the first experimental year. All animals were given the same amount of concentrate (2 kg/day of a commercial mixture containing 11.7 MJ metabolizable energy/kg and 125 g digestible protein/kg). 1"4 degradation was estimated according to the method of Yousef and Johnson (6). The fractional turnover rate and the apparent distribution volume for T4 was measured by injecting ~31I-T4 into the jugular vein. Blood samples were taken at 24, 48, 60 and 72 hours. After an equilibrium time of 24 hours, the ~3~I-T4 was eliminated from the body by first-order kinetics. As described by Yousef and Johnson (6), the T4 fractional turnover rate (K/day) and apparent T4 distribution volume (1) could be estimated by measuring isotope activity in the blood samples. T4 levels ( n m o l / 1 ) in plasma were measured by radioimmunoassay, as described by Tveit and Almlid (7). The standard deviation within each series varied from 5 to 10%. Series in which the mean of 3 control samples deviated by more than 10% from the expect ed mean were not used and a new assay was performed. T4 degradation (nmol/day) was calculated as a product of the T4 level in plasma, apparent distribution volume, and fractional turnover rate. T4 degradation per 100 kg live weight (nmol/day/100kg) was also calculated. To facilitate measurement of the T4 degradation, the 70 heifers used each year were divided into two groups according to age. The older group was tested first and the younger group about two weeks later. Thyroid activity was repeatedly measured in years 1, 2, 7 and 8 at 1 to 3 month intervals. The first ordinary test was always made in November/December and the repeat measurements in January/February. The production traits analyzed were daily roughage dry matter intake (kg), daily weight gain (g), and roughage dry matter intake/kg weight gain (kg) during the period from 12 to 15 months of age. Even though the energy
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c o n t e n t in the grass silage varied s o m e w h a t f r o m year to year, during any p a r t i c u l a r year, the animals all r e c e i v e d silage of e q u a l quality at the same time. S t a t i s t i c a l m e t h o d s . Repeatability or c o r r e l a t i o n b e t w e e n r e p e a t measuremenus o f the thyroid activity traits in the same animals w e r e c a l c u l a t e d b y the m e t h o d o f intra-class (intra-heifer) c o r r e l a t i o n (8). The m o d e l i n c l u d e d the g r o u p s o f heifers m e a s u r e d s i m u l t a n e o u s l y and live w e i g h t as a covariate (using the m o n t h l y w e i g h i n g closest to the date of thyroid activity d e t e r m i n a t i o n ) . Heritabilities and g e n e t i c correlations w e r e e s t i m a t e d f r o m sire c o m p o n e n t s and analyzed a c c o r d i n g to the m e t h o d of least.square analysis of data w i t h u n e q u a l subclasses using the LSML 76 p r o g r a m (9). The f o l l o w i n g m o d e l was a s s u m e d to d e s c r i b e the data for the thyroid traits: Ytj~ = ~t + al +Sq + bk + ~(X~jk'X) + ejjk where: Yqk is ~t is a~ is Slj is bk is [3 is Xqk is eljk is
the o b s e r v a t i o n for a trait on the ijk t" heifer, the general mean, the effect of the i t" g r o u p of sires (high or l o w t h y r o x i n e degradation), the effect o f the jth sire w i t h i n the i th group, the effect of the k th b a t c h of T4. activity d e t e r m i n a t i o n , the linear regression on age, the age at d e t e r m i n a t i o n of the ijk t" animal, and a residual r a n d o m term.
The effect of sire was r e g a r d e d as r a n d o m and the o t h e r effects as fixed. T h y r o x i n e d e g r a d a t i o n data, e x p r e s s e d as deviation f r o m b a t c h average, w e r e also available for the 20 sires in the e x p e r i m e n t . Therefore, a s e c o n d estimate of heritability for thyroxine d e g r a d a t i o n c o u l d b e m a d e f r o m a regression of daughters on sire. RESULTS A N D DISCUSSION M e a n s a n d s t a n d a r d d e v i a t i o n . Overall means and standard deviations on a w i t h i n - b a t c h basis are s h o w n in Table 1. The m e a n s and standard deviations w e r e in reasonable a g r e e m e n t w i t h earlier reports ( 3 , 5 , 7 ) . The T4 p l a s m a levels, a p p a r e n t distribution v o l u m e , and cons e q u e n t T4 d e g r a d a t i o n r e p o r t e d in the first t w o of these three earlier studies, w e r e slightly higher than the findings in the p r e s e n t study. The T4 fractional t u r n o v e r rates w e r e v e r y similar in all four studies. TABLe 1. OVERALL MEANS (X) AND STANDARD DEVIATION (S.D.) ON A WITHIN BATCH BASIS FOR THYROXINE AND PRODUCTION TE~dTS IN HEIFERS. AGE AND Live WEIGHT ON AN OVERALL BASIS,
T4 plasma level (nmol/1) T, distribution volume (1) T, fractional turnover rate (K/day) T, degradation (nmol/day) T, degrad./10Okg (nmol/day/100 kg) Roughage dry matter intake (kg/day) Daily weight gain (g) Roughage d.m./kg weight gain (kg) Age at start of determination of roughage intake (days) Age at determination of thyroid traits (days) Live weight at determination of thyroid traits (kg)
80.9 26.9 O.339 729.6 213.2 4.7 777.4 6.3
S.D. 11.1 3.18 0.055 129.4 37.9 0.39 101.2 1.2
336
40
436
87
320
34.1
204
STANDAL, TVEIT AND SVENDSEN T~mL~ 2. REPEATABILITY OF THYROID ACTIVITY DETERMINATION. ALL TPOOTS EXCEPT FOR APPARENT DISTRIBUTION VOLUME ARE CORRECTED FOR LIVE WEIGHT. Years
T4 T4 T4 T4
plasma level distribution volume fractional turnover rate degradation
1977-78 0.33 0.42 0.32 0.33
1978-79 0.65 0.44 0.00 0.05
1982-83 0.64 0.40 0.42 0.55
1983-84 0.75 0.55 0.45 0.38
Mean 0.59 0.45 0.30 0.33
R e p e a t a b i l i t y . Intra-heifer correlations for repeat recordings of thyroid activity traits in the years with repeat recordings are given in Table 2. Live weight was included in all the models except the one for T4 distribution volume. The estimated repeatabilities showed considerable year-to-year variation, and on average they were lower than those found by Joakimsen et al (3). The values from the second year were especially low for the T4 fractional turnover rate and T4 degradation. The reasons for this are not known, although several factors may have affected these values. The period of time elapsing between repeat measurements was the longest (3 months) that year. Quantitative injection of isotope solutions was difficult in fractious animals and this difficulty wo u ld have affected the accuracy of the measurements. In addition, ambient temperature and feeding are environmental factors that are known to affect T4 levels and secretion. Refsal et al (10) have described an ambient temperature of 20-25C as providing a thermoneutral state. Given the animals in this experiment were housed at this temperature or somewhat below, temperature should probably have not caused much 3"4variation. However, variable roughage quality and appetite cannot be excluded. Short periods of starvation have been shown to result in decreased T4 secretion and lower T4 levels in plasma (7). These results indicate that, if thyroid activity is to be used as an aid in selecting breeding animals, repeated measurements are necessary before a performance test can be reliable. H e r i t a b i l i t i e s a n d g e n e t i c c o r r e l a t i o n s . The effect of grouping the sires according to their T4 degradation was significant only for the serum T4 level and accounted for about 2 percent of the total variation in this trait. The effect of batch (occasion of determination) was highly significant for all thyroid traits and supported the necessity of either including this effect in the model or expressing the values as deviations from batch average. Heritabilities estimated from sire components are given in Table 3. The heritability estimates for the thyroid traits are 0.1-0.4. Though some are lower than those found in the Danish investigation of young bulls (5), for T4 degradation/100 kg live weight, the estimates are very similar. This is the trait which Joakimsen (3) and Sorensen (5) have suggested should be employed as a predictor for milk production. TABL~ 3. HERITABILITIES + STANDARDERRORS. h2
T4 plasma level T4 apparent distribution volume T4 fractional turnover rate T4 degradation 1"4 degradation/100 kg Roughage dry matter intake Daily weight gain Roughage dry matter/kg weight gain • negative sire c o m p o n e n t
0.22 0.26 0.39 0.09 0.24 0.16 0.18
_+ 0.12 + 0.13 + 0.16 -+ 0.09 _+ 0.12 + 0.10 _+ 0.11
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TABLE4. PHENOTYPIC(rp) ANDGENETIC(rl) CORRELATIONBETWEENPRODUCTIONTRAlTSANDTHYROID ACTIVITYT~ITS (OBSERVATIONSCORRECTEDTO SAMEAGE). Roushatge intake Daily ~gain rp rs rp rs T4 plasma level 0.05 0.18_+0.44 0.11 -0.21 _+0.42 1"4 distribution volume 0.38 0.00 _+0.44 0.23 0.23 +-0.40 T4 fractional turnover rate -0.10 -0.32 -+0.39 -0.05 -0.04 _+0.39 1"4 degradation 0.21 -0.25 +0.54 0.14 -0.01 "--0.55 T~ degradation/100 kg -0.15 -0.47 +-0.43 0.03 -0.20 _ 0.42 Daily weight gain 0.32 1.00 --,0.24 AS described u n d e r statistical methods, the m o d e l includes the g r o u p o f sires as a major classification. This inclusion eliminates the effect of selection and may, in addition, r e d u c e the normal variation b e t w e e n sires. This l o w e r variation in turn reduces the sire c o m p o n e n t s and the estimated heritabilities for the thyroid activity traits. For this reason, the heritabilities in this study may be slightly underestimated. The genetic variation for roughage feed c o n v e r s i o n was very low (no sire c o m p o n e n t ) . Table 4 shows that the n u m e r a t o r and d e n o m i n a t o r o f the feed c o n v e r s i o n seem to be genetically the same trait, with an estimated genetic correlation of 1. This correlation is p r o b a b l y the reason for the sire c o m p o n e n t b e i n g 0. Genetic studies of feed efficiency in y o u n g heifers are scarce and have not been f o u n d in the literature. It may be e x p e c t e d that the genetic variation in feed efficiency is low at this stage of maturity, w h e n only mariginal fat d e p o s i t i o n has taken place. The heritability of the thyroxine degradation, as estimated in the alternative w a y as a regression of daughters on sire, was h 2 ---- 0.04 + .03. The n u m b e r o f sires was low, making this estimate rather unreliable. Genetic and p h e n o t y p i c correlations b e t w e e n r o u g h a g e dry matter intake, daily w e i g h t gain and the thyroid activity traits are given in Table 4. Both the p h e n o t y p i c and the genetic correlations were generally small and non-significant. The genetic correlations b e t w e e n a d lib roughage dry matter intake and the traits describing degradation of T4 are all negative, while the correlations with daily gain were almost zero. Danish results (5) also indicated a lower feed intake for animals with high T4 degradation, t h o u g h a higher daily w e i g h t gain was f o u n d in these animals. H o r m o n e levels are influenced by n u m e r o u s e n v i r o n m e n t a l factors, and genetic-environmental interactions can be expected. T h o u g h g e n e t i c parameters for h o r m o n a l traits, estimated u n d e r strictly controlled e n v i r o n m e n t a l conditions, may have only small standard errors, the estimates might not be valid u n d e r different conditions. Because the e x p e r i m e n t described in this p a p e r lasted 8 years, some o f the r a n d o m environmental variation w h i c h is to be e x p e c t e d u n d e r farm c o n d i t i o n s has been included. FOOTNOTES Address all correspondence to: Borghild Tveit, Department of Animal Genetics and Breeding, Agricultural University of Norway, Box 24, 1432 As-NLH,Norway. REFERENCES
1. Fabry J. Thyroid hormones and daily gain in cattle. Anim Prod 36:355-361, 1983. 2. Bobek S, Kacinsha M, Zapletal P. Thyroxine and triiodo-thyronine concentration in the serum of bull-calves and its dependence on season of birth and relationship to body weight gain. Zentralblatt fur Veterinarmedizin A27 (9/10):697-701, 1980.
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3. Joakimsen O, Steenberg K, Lien H, Theodorsen L. Genetic relationship between thyroxine degradation and fat corrected milk yield in cattle. Acta Agric Scand 21:121-124, 1971. 4. Joakimsen O. Estimates of thyroid activity as predictors of breeding value for milk production in cattle. FAAP-Congress, Warsaw, 1975. 5. Sorensen MT, Kruse V, Bech Andersen B. Thyroxine degradation rate in young bulls of Danish dual-purpose breeds. Genetic relationship to weight gain, feed conversion and breeding value for better fat production. Livestock Prod Sci 8:399-406, 1981. 6. Yousef MK, Johnson HD. A rapid method for estimation of thyroxine secretion rate of cattle. J Anim Sci 26:1108-1112, 1967. 7. Tveit B, Almlid T. "1"4degradation rate and plasma levels of TSH and thyroid hormones in ten young bulls during feeding condition and 48 hr of starvation. Acta Endocrinol 93:435-439, 1981. 8. Steel, RGD, Torrie JH. Principles and procedures of statistics, with special reference to the biological sciences. McGraw-Hill Book Company, New York, 1960. 9. Harvey WR. Users Guide for LSML76. Mixed Model Least-squares and Maximum Likelihood Computer Program. Ohio State University, 1977. 10. Refsal KR, Nachreiner RF, Anderson CR. Relationship of season, herd, lactation, age and pregnancy with serum thyroxine and triiodothyronine in Holstein cows. Domestic Anita Endocrinol 1:225-234, 1984.
Vol, 4(3):201-206, 1987
THYROID ACTIVITY IN RELATION TO FEED INTAKE, GROWTH RATE AND FEED CONVERSION IN GROWING HEIFERS Nils Standal, Borghild Tveit and Morten Svendsen Agricultural University of Norway Department of Animal Science Box 25, 1432 As-NLH Received June 2, 1986
ABSTRACT Phenotypic and genetic parameters for thyroid activity (T~ serum level, T4 apparent distribution volume, T4 fractional turnover rate and T4 degradation), and for certain production traits (roughage dry matter intake, daily weight gain and roughage dry matter/kg weight gain), were investigated in cattle. In the experiment, 480 growing heifers were studied, daughters of 20 AI sires previously tested for thyroid activity. Repeatabilities for thyroid traits 2-3 months apart varied, with an average 0.3-0.6 for the different traits. Heritability estimates based on sire components were 0.1-0.4 for the thyroid traits, 0.16 +. 10 for roughage intake and 0.18 _. 11 for daily gain. The sire component for feed efficiency (roughage dry matter/kg weight gain) was 0, and genetic correlations between thyroid traits and the production traits in growing heifers were low with large standard errors. INTRODUCTION Thyroid activity has been one of the biological features studied in the search for physiological/endocrinological criteria to aid selection for production traits in cattle. The thyroid hormones are known to be important for milk production and are also vital for normal growth and development. Conflicting results have been reported in the literature about the relationship between different thyroid activity parameters and growth rate. Fabry (1) found a highly significant positive correlation (0.79) between daily live weight gain in a 12-month period and the serum thyroxine (T4) level at 15 to 20 days of age. In a trial under farm conditions, the same author (1) found highly significant negative correlations between T4 levels and daily weight gain during a similar period. Bobek et al (2) reported positive correlations between body weight gain from 28 to 104 days of age and T3 (0,484) and 1"4 (0,175) serum levels. Several reports have been published concerning the connection between thyroid activity and milk production traits. Joakimsen et al (3) suggested that T4 degradation might be a useful index of thyroid activity, and found a genetic correlation of 0.42 between this index in sires and fat-corrected milk yield in their daughters. In a later paper, Joakimsen (4) confirmed that there was also a positive genetic correlation when thyroxine degradation was measured on young bulls of 4-12 months of age. Similar results were reported by Sorensen et al (5). Joakimsen (4) did, however, express a need for caution in using T4 degradation as an index for pre-selection of bulls, drawing attention to the profound effect of the thyroid hormones on energy metabolism and the effect that selection for thyroid activity might have in increasing maintenance requirements. The purpose of this experiment was to study genetic and phenotypic variation and covariation in thyroid activity parameters and production traits in dairy Copyright O 1987 by DOMENDO,INC.
201
0739-7240/87/$3.00
202
STANDAL, TVEIT AND SVENDSEN
cattle. The production traits measured were daily weight gain, feed conversion and daily a d lib roughage dry matter intake in the period from 12 to 15 months of age. MATERIALS A N D METHODS
The 20 AI bulls used as sires in the experiment all had an above-average predicted breeding value for milk production based on progeny tests. All had been tested for thyroid activity twice between the ages of 4 and 12 months (4), ten had a higher T4 degradation rate than average, the remaining 10 a lower degradation rate than average. Each year from 1977 to 1985 inclusive (years 1 to 8), 3-4 daughters of each bull (about 70 heifers per year) were chosen as the experimental animals. Altogether 480 heifers com pl e t e d the experiment. They entered the experiment at 9-12 months of age in September each year and were stall-fed for 9 months, after which they were let out on pasture before continuing the experiment during their first lactation. Growth rate calculations were based on monthly weighings of the animals. Individual feed recording was performed 4 days each week for 12-16 weeks in the period from October to January. During that time the animals were individually fed grass silage twice a day. The amounts fed and recorded were intended to be a d lib. The silage not consumed was removed and recorded every second day. It proved necessary to offer in addition an ammonia-treated barley straw from January until the end of the indoor season in order to make the grass silage last, though this could not be recorded with the same precision. No feed recording was performed during the first experimental year. All animals were given the same amount of concentrate (2 kg/day of a commercial mixture containing 11.7 MJ metabolizable energy/kg and 125 g digestible protein/kg). 1"4 degradation was estimated according to the method of Yousef and Johnson (6). The fractional turnover rate and the apparent distribution volume for T4 was measured by injecting ~31I-T4 into the jugular vein. Blood samples were taken at 24, 48, 60 and 72 hours. After an equilibrium time of 24 hours, the ~3~I-T4 was eliminated from the body by first-order kinetics. As described by Yousef and Johnson (6), the T4 fractional turnover rate (K/day) and apparent T4 distribution volume (1) could be estimated by measuring isotope activity in the blood samples. T4 levels ( n m o l / 1 ) in plasma were measured by radioimmunoassay, as described by Tveit and Almlid (7). The standard deviation within each series varied from 5 to 10%. Series in which the mean of 3 control samples deviated by more than 10% from the expect ed mean were not used and a new assay was performed. T4 degradation (nmol/day) was calculated as a product of the T4 level in plasma, apparent distribution volume, and fractional turnover rate. T4 degradation per 100 kg live weight (nmol/day/100kg) was also calculated. To facilitate measurement of the T4 degradation, the 70 heifers used each year were divided into two groups according to age. The older group was tested first and the younger group about two weeks later. Thyroid activity was repeatedly measured in years 1, 2, 7 and 8 at 1 to 3 month intervals. The first ordinary test was always made in November/December and the repeat measurements in January/February. The production traits analyzed were daily roughage dry matter intake (kg), daily weight gain (g), and roughage dry matter intake/kg weight gain (kg) during the period from 12 to 15 months of age. Even though the energy
THYROID ACTIVITY IN GROWING HEIFERS
203
c o n t e n t in the grass silage varied s o m e w h a t f r o m year to year, during any p a r t i c u l a r year, the animals all r e c e i v e d silage of e q u a l quality at the same time. S t a t i s t i c a l m e t h o d s . Repeatability or c o r r e l a t i o n b e t w e e n r e p e a t measuremenus o f the thyroid activity traits in the same animals w e r e c a l c u l a t e d b y the m e t h o d o f intra-class (intra-heifer) c o r r e l a t i o n (8). The m o d e l i n c l u d e d the g r o u p s o f heifers m e a s u r e d s i m u l t a n e o u s l y and live w e i g h t as a covariate (using the m o n t h l y w e i g h i n g closest to the date of thyroid activity d e t e r m i n a t i o n ) . Heritabilities and g e n e t i c correlations w e r e e s t i m a t e d f r o m sire c o m p o n e n t s and analyzed a c c o r d i n g to the m e t h o d of least.square analysis of data w i t h u n e q u a l subclasses using the LSML 76 p r o g r a m (9). The f o l l o w i n g m o d e l was a s s u m e d to d e s c r i b e the data for the thyroid traits: Ytj~ = ~t + al +Sq + bk + ~(X~jk'X) + ejjk where: Yqk is ~t is a~ is Slj is bk is [3 is Xqk is eljk is
the o b s e r v a t i o n for a trait on the ijk t" heifer, the general mean, the effect of the i t" g r o u p of sires (high or l o w t h y r o x i n e degradation), the effect o f the jth sire w i t h i n the i th group, the effect of the k th b a t c h of T4. activity d e t e r m i n a t i o n , the linear regression on age, the age at d e t e r m i n a t i o n of the ijk t" animal, and a residual r a n d o m term.
The effect of sire was r e g a r d e d as r a n d o m and the o t h e r effects as fixed. T h y r o x i n e d e g r a d a t i o n data, e x p r e s s e d as deviation f r o m b a t c h average, w e r e also available for the 20 sires in the e x p e r i m e n t . Therefore, a s e c o n d estimate of heritability for thyroxine d e g r a d a t i o n c o u l d b e m a d e f r o m a regression of daughters on sire. RESULTS A N D DISCUSSION M e a n s a n d s t a n d a r d d e v i a t i o n . Overall means and standard deviations on a w i t h i n - b a t c h basis are s h o w n in Table 1. The m e a n s and standard deviations w e r e in reasonable a g r e e m e n t w i t h earlier reports ( 3 , 5 , 7 ) . The T4 p l a s m a levels, a p p a r e n t distribution v o l u m e , and cons e q u e n t T4 d e g r a d a t i o n r e p o r t e d in the first t w o of these three earlier studies, w e r e slightly higher than the findings in the p r e s e n t study. The T4 fractional t u r n o v e r rates w e r e v e r y similar in all four studies. TABLe 1. OVERALL MEANS (X) AND STANDARD DEVIATION (S.D.) ON A WITHIN BATCH BASIS FOR THYROXINE AND PRODUCTION TE~dTS IN HEIFERS. AGE AND Live WEIGHT ON AN OVERALL BASIS,
T4 plasma level (nmol/1) T, distribution volume (1) T, fractional turnover rate (K/day) T, degradation (nmol/day) T, degrad./10Okg (nmol/day/100 kg) Roughage dry matter intake (kg/day) Daily weight gain (g) Roughage d.m./kg weight gain (kg) Age at start of determination of roughage intake (days) Age at determination of thyroid traits (days) Live weight at determination of thyroid traits (kg)
80.9 26.9 O.339 729.6 213.2 4.7 777.4 6.3
S.D. 11.1 3.18 0.055 129.4 37.9 0.39 101.2 1.2
336
40
436
87
320
34.1
204
STANDAL, TVEIT AND SVENDSEN T~mL~ 2. REPEATABILITY OF THYROID ACTIVITY DETERMINATION. ALL TPOOTS EXCEPT FOR APPARENT DISTRIBUTION VOLUME ARE CORRECTED FOR LIVE WEIGHT. Years
T4 T4 T4 T4
plasma level distribution volume fractional turnover rate degradation
1977-78 0.33 0.42 0.32 0.33
1978-79 0.65 0.44 0.00 0.05
1982-83 0.64 0.40 0.42 0.55
1983-84 0.75 0.55 0.45 0.38
Mean 0.59 0.45 0.30 0.33
R e p e a t a b i l i t y . Intra-heifer correlations for repeat recordings of thyroid activity traits in the years with repeat recordings are given in Table 2. Live weight was included in all the models except the one for T4 distribution volume. The estimated repeatabilities showed considerable year-to-year variation, and on average they were lower than those found by Joakimsen et al (3). The values from the second year were especially low for the T4 fractional turnover rate and T4 degradation. The reasons for this are not known, although several factors may have affected these values. The period of time elapsing between repeat measurements was the longest (3 months) that year. Quantitative injection of isotope solutions was difficult in fractious animals and this difficulty wo u ld have affected the accuracy of the measurements. In addition, ambient temperature and feeding are environmental factors that are known to affect T4 levels and secretion. Refsal et al (10) have described an ambient temperature of 20-25C as providing a thermoneutral state. Given the animals in this experiment were housed at this temperature or somewhat below, temperature should probably have not caused much 3"4variation. However, variable roughage quality and appetite cannot be excluded. Short periods of starvation have been shown to result in decreased T4 secretion and lower T4 levels in plasma (7). These results indicate that, if thyroid activity is to be used as an aid in selecting breeding animals, repeated measurements are necessary before a performance test can be reliable. H e r i t a b i l i t i e s a n d g e n e t i c c o r r e l a t i o n s . The effect of grouping the sires according to their T4 degradation was significant only for the serum T4 level and accounted for about 2 percent of the total variation in this trait. The effect of batch (occasion of determination) was highly significant for all thyroid traits and supported the necessity of either including this effect in the model or expressing the values as deviations from batch average. Heritabilities estimated from sire components are given in Table 3. The heritability estimates for the thyroid traits are 0.1-0.4. Though some are lower than those found in the Danish investigation of young bulls (5), for T4 degradation/100 kg live weight, the estimates are very similar. This is the trait which Joakimsen (3) and Sorensen (5) have suggested should be employed as a predictor for milk production. TABL~ 3. HERITABILITIES + STANDARDERRORS. h2
T4 plasma level T4 apparent distribution volume T4 fractional turnover rate T4 degradation 1"4 degradation/100 kg Roughage dry matter intake Daily weight gain Roughage dry matter/kg weight gain • negative sire c o m p o n e n t
0.22 0.26 0.39 0.09 0.24 0.16 0.18
_+ 0.12 + 0.13 + 0.16 -+ 0.09 _+ 0.12 + 0.10 _+ 0.11
THYROID ACTIVITY IN GROWING HEIFERS
205
TABLE4. PHENOTYPIC(rp) ANDGENETIC(rl) CORRELATIONBETWEENPRODUCTIONTRAlTSANDTHYROID ACTIVITYT~ITS (OBSERVATIONSCORRECTEDTO SAMEAGE). Roushatge intake Daily ~gain rp rs rp rs T4 plasma level 0.05 0.18_+0.44 0.11 -0.21 _+0.42 1"4 distribution volume 0.38 0.00 _+0.44 0.23 0.23 +-0.40 T4 fractional turnover rate -0.10 -0.32 -+0.39 -0.05 -0.04 _+0.39 1"4 degradation 0.21 -0.25 +0.54 0.14 -0.01 "--0.55 T~ degradation/100 kg -0.15 -0.47 +-0.43 0.03 -0.20 _ 0.42 Daily weight gain 0.32 1.00 --,0.24 AS described u n d e r statistical methods, the m o d e l includes the g r o u p o f sires as a major classification. This inclusion eliminates the effect of selection and may, in addition, r e d u c e the normal variation b e t w e e n sires. This l o w e r variation in turn reduces the sire c o m p o n e n t s and the estimated heritabilities for the thyroid activity traits. For this reason, the heritabilities in this study may be slightly underestimated. The genetic variation for roughage feed c o n v e r s i o n was very low (no sire c o m p o n e n t ) . Table 4 shows that the n u m e r a t o r and d e n o m i n a t o r o f the feed c o n v e r s i o n seem to be genetically the same trait, with an estimated genetic correlation of 1. This correlation is p r o b a b l y the reason for the sire c o m p o n e n t b e i n g 0. Genetic studies of feed efficiency in y o u n g heifers are scarce and have not been f o u n d in the literature. It may be e x p e c t e d that the genetic variation in feed efficiency is low at this stage of maturity, w h e n only mariginal fat d e p o s i t i o n has taken place. The heritability of the thyroxine degradation, as estimated in the alternative w a y as a regression of daughters on sire, was h 2 ---- 0.04 + .03. The n u m b e r o f sires was low, making this estimate rather unreliable. Genetic and p h e n o t y p i c correlations b e t w e e n r o u g h a g e dry matter intake, daily w e i g h t gain and the thyroid activity traits are given in Table 4. Both the p h e n o t y p i c and the genetic correlations were generally small and non-significant. The genetic correlations b e t w e e n a d lib roughage dry matter intake and the traits describing degradation of T4 are all negative, while the correlations with daily gain were almost zero. Danish results (5) also indicated a lower feed intake for animals with high T4 degradation, t h o u g h a higher daily w e i g h t gain was f o u n d in these animals. H o r m o n e levels are influenced by n u m e r o u s e n v i r o n m e n t a l factors, and genetic-environmental interactions can be expected. T h o u g h g e n e t i c parameters for h o r m o n a l traits, estimated u n d e r strictly controlled e n v i r o n m e n t a l conditions, may have only small standard errors, the estimates might not be valid u n d e r different conditions. Because the e x p e r i m e n t described in this p a p e r lasted 8 years, some o f the r a n d o m environmental variation w h i c h is to be e x p e c t e d u n d e r farm c o n d i t i o n s has been included. FOOTNOTES Address all correspondence to: Borghild Tveit, Department of Animal Genetics and Breeding, Agricultural University of Norway, Box 24, 1432 As-NLH,Norway. REFERENCES
1. Fabry J. Thyroid hormones and daily gain in cattle. Anim Prod 36:355-361, 1983. 2. Bobek S, Kacinsha M, Zapletal P. Thyroxine and triiodo-thyronine concentration in the serum of bull-calves and its dependence on season of birth and relationship to body weight gain. Zentralblatt fur Veterinarmedizin A27 (9/10):697-701, 1980.
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3. Joakimsen O, Steenberg K, Lien H, Theodorsen L. Genetic relationship between thyroxine degradation and fat corrected milk yield in cattle. Acta Agric Scand 21:121-124, 1971. 4. Joakimsen O. Estimates of thyroid activity as predictors of breeding value for milk production in cattle. FAAP-Congress, Warsaw, 1975. 5. Sorensen MT, Kruse V, Bech Andersen B. Thyroxine degradation rate in young bulls of Danish dual-purpose breeds. Genetic relationship to weight gain, feed conversion and breeding value for better fat production. Livestock Prod Sci 8:399-406, 1981. 6. Yousef MK, Johnson HD. A rapid method for estimation of thyroxine secretion rate of cattle. J Anim Sci 26:1108-1112, 1967. 7. Tveit B, Almlid T. "1"4degradation rate and plasma levels of TSH and thyroid hormones in ten young bulls during feeding condition and 48 hr of starvation. Acta Endocrinol 93:435-439, 1981. 8. Steel, RGD, Torrie JH. Principles and procedures of statistics, with special reference to the biological sciences. McGraw-Hill Book Company, New York, 1960. 9. Harvey WR. Users Guide for LSML76. Mixed Model Least-squares and Maximum Likelihood Computer Program. Ohio State University, 1977. 10. Refsal KR, Nachreiner RF, Anderson CR. Relationship of season, herd, lactation, age and pregnancy with serum thyroxine and triiodothyronine in Holstein cows. Domestic Anita Endocrinol 1:225-234, 1984.