Beef Improvement New Zealand Inc. 1 Individual cow evaluation for efficiency Summary Cow and calf data from 32 -years of commercial beef s in Canterbury New Zealand was used to determine the relative efficiency of individual cows. Some of the data was from whole s and other s only recorded first calving heifers. Whole s Average scale weight of calves at weaning varied by more than 100 kgs between s (183.0 to 290.3 kgs). When corrected for age and sex of calf and age of dam, the average calf rearing potential ( 200d wt ) of different s varied substantially ranging from 165.4 to 270.0 kgs. Average autumn cow scale weight also varied considerably with the lightest having an average weight of 415.1 kgs and the heaviest 640.9 kgs. Average autumn body condition score of cows in different -years varied from 3.1 to 7.7 (on a 1 to 9 scale) although there was probably considerable variation in farmer estimation of condition scores. Cow weights adjusted for body condition score (BCS) and age of cow ( BCS5MCW ) varied from 415 to 766 kgs. The average net energy requirements for maintenance and activity of cows ( Maint + ) ranged from 4,853 to 8,721 Mcal Net Energy suggesting substantial differences exist in the cost of maintaining different s. The average potential calf value (200d wt multiplied by $2.00 per kg) was related to total net energy requirement of each cow calf pair to calculate an efficiency estimate ( calf $ per unit NE ). There was considerable variation between -years with a range of more than $118 between the extremes: $345 per unit of NE in the least efficient and over $463 in the most efficient. Within variation suggested culling of the bottom 10% of cows would raise likely future calf $ per unit NE by $8.39 after correction for repeatability. Limited data from repeat records of the same individual cows in different years produced wide ranging estimates of the repeatability of both 200d wt and calf $ per unit NE. Application of the same model to better quality data from Whatawhata research station produced more consistent results that were compatible with repeatability estimates of 200d wt and mature cow weight found in the literature. Repeatability estimates for 200d weight derived from the Whatawhata data for 200d wt averaged 0.63 and ranged from 0.45 to 0.76. Whatawhata repeatability estimates for calf $ per unit NE averaged 0.46 and ranged from 0.28 to 0.54. First calving heifers Herd average age at weaning of calves out of first calving heifers ranged from 164 to 236 days suggesting comparison of averages calf weaning weight without adjustment for age of calf may be as much a comparison of age at weaning as it is of the calf rearing ability of the heifers. Average autumn scale wt of rising three year heifers varied by over 100 kgs between farms and average BCS varied by over 3.0 units on a 1 to 9 scale. When 200d wt of heifers calves was compared with the autumn scale wt of the heifers there was little relationship with heifer weigh explaining only 10% of the variation of calf 200d wt. Culling the bottom half of R 3yr heifers on the basis of their first calf production increased the likely future calf $ per unit NE of replacements by $21.33.
2 Materials and methods Data was obtained from thirty two different -years. Many s only recorded first calving heifers but a number collected data from all of the cows in the. Some s recorded calving date, birth weight and weaning weight of calves while others recorded calf marking and weaning weight. Cow weights and body condition scores were recorded at weaning. In 2006 and 2007 all dam parentage was determined by visual observation either at birth or after marking. In 2008 fifteen s opted to determine parentage by DNA profiling and submitted skin samples to the Gene Marker Lab at Lincoln University. Regrettably GML s efforts to determine parentage were unsuccessful and none of the 15 s had any record of dam parentage for the 2008 calving. The calf rearing ability of each cow ( 200d wt ) was calculated by adjusting each calf s weaning weight for non-repeatable effects (age and sex of calf and age of cow). For s recording calving date each calf s birth weight (either recorded or assumed) was subtracted from its weaning weight to produce a gain between birth and weaning which was then divided by the age at weaning to produce an average daily gain (ADG) from birth to weaning. The ADG was multiplied by 200 to obtain a gain to 200 days which was then adjusted for sex of calf and age of dam according to the modifications of the adjustments provided by Beef Improvement Ontario which are given in Appendix 1. The BIO adjustments were modified so that instead of adjustment to an average calf the adjustment was to that of a 200day old heifer calf out of a five year old cow. Since some of the s involved in this study retained all bull calves as entires, some castrated all male calves and some castrated only some of the male calves, it was decided to use heifer calves as the standard and the BIO recommendations were modified accordingly. Known birth weight was adjusted for sex of calf and age of dam according to the BIO recommendations or (if actual birth weight was not available) the BIO average 5yr heifer calf birth wt was substituted. One or the other was then added to the adjusted gain to 200 days to produce a 200d wt. For the s not recording calving date, each calf s marking weight was subtracted from its weaning weight to obtain a ADG marking to weaning which was then multiplied by 200 to produce a gain to 200d figure that was then adjusted for sex of calf and age of dam using the same modified BIO adjustments. A 200 day weight was then calculated by adding the breed average birth wt for heifer calves out of five year old cows to the adjusted gain to 200d to produce a 200d wt. Whatawhata data with calving, marking and weaning data suggested a high correlation between 200d wt calculated by the two methods. Comparison of 200d wt of calves calculated from the average daily gain between birth and weaning and between marking and weaning year r Whatawhata 1995 0.98 Whatawhata 1996 0.96 Whatawhata 1997 0.93 Whatawhata 2000 0.99 Whatawhata 2001 0.88
All cows were weighed and assessed for body condition score by the farmers in the autumn using a 1 to 9 scale. Cow weight was adjusted to a standard BCS of 5.0 BCS5Wt according to published recommendations (National Research Council, 2000). Since calf weights were adjusted to an equivalent of calves out of five year old cows, cow weights were also adjusted for age of cow. Each cow s five year old weight was assumed to be proportional to her weight as a younger cow based on her relative ranking within age group, i.e. cows lighter than average (after adjustment for BCS) as two year olds were assumed to be proportionally lighter as five year old cows. Cow weight adjusted for BCS and age of cow was labelled BCS5MCW. The total net energy requirement of each cow/calf pair was estimated from the NRC Nutrient Requirements of Beef Cattle computer program (National Research Council, 2000) which requires inputs of animal data (sex, age, weight, body condition score and three generations of breed), management information (whether animals are implanted, on pasture or feedlot, on hill or flat country) and environmental conditions (average day and nighty temperature and wind velocity). BCS5MCW was converted to metabolic body wt and then used to estimate each cow s maintenance and activity requirements which were adjusted for level of production according to accepted formulas(national Research Council, 2000). Energy requirements for pregnancy were estimated from cow size. Energy requirements for lactation were estimated from NRC tables that use BCS5 cow weight as an indication of cow genetics for size and growth and calf 200d wt as an estimation of milk production of the cow. The assumption being that for a given cow weight a larger calf weight is the result of greater milk production by the cow. Calf energy requirements were estimated from modifications of the NRC model for maintenance, activity and growth. Each cow s calf rearing ability (200d wt) was related to the total net energy requirement of the cow calf pair and expressed as the value of calf production each cow would have achieved if she had been allocated a standard amount of energy which was set at 8,500 Mcal of net energy. Finally each cow s calf value/8.500 Mcal NE was expressed as a deviation from the year mean each cow was said to have produced X number of dollars more or less than the average cow from that that year. Each cow s 200d wt was multiplied by a repeatability estimate derived from project data to produce a Most Probable Producing Ability calf value which is reported to be the best estimate of future production (Kress & Burfening, 1972; Lush, 1945). Repeat records from commercial s were used in the estimation of the repeatability of efficiency as well. 3
Results Whole Herd calving data Usable data was available from 2,283 calves from 22 -years. Herd average calf scale weaning weight again varied by over 100 kgs between the different s. 4 300 whole data calf scale wt at weaning 250 ave wn wt 200 150 100 WC6 WX8 Adjusted gain to 200 days of age ranged from 129.4 to 234.0 kgs and average 200d wt similarly ranged f 165.4 to 270.0. Within variation was also large for all calf traits. ave 200d wt 300 250 200 150 BINZ whole data 200 day weight WM6 WX8 WC6 WM6 Herd average cow autumn scale weight varied by more than 200 kgs with the lightest average 415.0 and heaviest 640.9 kgs. Herd average BCS ranged from 3.1 to 7.7 but probably suffered from different standards applied by individual farmers. Herd average cow weight adjusted for BCS and age of cow showed large variation with a range of more than 350 kgs between the smallest and largest averages.
5 800 BINZ whole data, BCS5 Mature Cow Wt ave BCS5MCW 700 600 500 400 WC6 WM6 Accordingly the average Net Energy required for maintenance and activity was nearly twice as large (8,721 Mcal) in the with the largest cows as it was in the with the smallest cows (4,853 Mcal). 8000 BINZ whole data, average NE required for maintenance and activity 7000 ave Maint+ 6000 5000 4000 The average dollar value of calves produced per unit of Net Energy ranged from $345 to $463. ave $/NE 500 450 400 350 WC6 BINZ whole data, $ calf revenue per 8,500 Mcal Net Energy WM6 300 WM6 WC6
6 Culling the bottom 10% of the cows on efficiency raised the average MPPA calf value by an average of $8.93. $15 BINZ whole data Improvement in $calf/unit NE improvement $10 $5 $0 Two year old heifer calving data Two year old heifer calving data was available from 23 -years. The average age of calves at weaning varied by over 70 days demonstrating the importance of correcting calf scale weight for age at weaning in order to make meaningful comparisons of average calf rearing ability of heifers in different s. The average scale weight of calves at weaning in different s varied by over 100 kgs. 270 BINZ 2yr heifer data: average calf scale weight at weaning 250 ave wn wt 230 210 190 170 150 Herd averages of adjusted gain to 200 days of age varied from 168.1 kgs to 241.8 and average 200d wts varied widely as well between s. BINZ 2yr heifer 200d wt 275 ave 200d 225 175
Rising three year heifer autumn scale weight also varied substantially between s with the mob of the smallest heifers barely averaging 425 kgs while the largest averaged over 550 kgs. Average body condition score ranged from 3.1 to 6.6. Heifer weight adjusted for BCS and age of heifer varied widely between s. 7 ave wt 600 550 500 450 400 ave BCS 7 6.5 6 5.5 5 4.5 4 3.5 3 2.5 BINZ scale weight of R 3yr heifers average autumn body condition score of R 3yr heifers The average net energy required for maintenance and activity of the heifers varied by over 30% between farms suggesting that the number of heifers capable of being maintained on different properties per unit of energy varied considerably between properties. ave Maint + 9000 8000 7000 6000 5000 average maintenance + activity Net Energy requirement of R 3yr heifers
Herd average values for $ of calf per unit of energy varied from $350 to $487. average $ calf revenue per 8,500 Mcal Net Energy 8 500 450 $ per NE 400 350 300 There was little relationship between the calf rearing potential (200d wt) of heifers in each -year and the autumn weight of the Rising 3 year heifers,. For nearly all of the s less than 10% of the variation in calf 200d wt was explained by the autumn weight of the heifer. 60% BINZ Percentage of variation of 200d wt of calves explained by its dam's R 3yr wt 50% % variation 40% 30% 20% 10% 0% Culling the bottom half of each -year group of heifers on the basis of their first calf 200d wt increased the -year average by between 10.8 and 49.2 kgs (average 21.3 kgs). Culling the bottom half increased the future most likely calf production (MPPA calf value ) by an average of $21.30 with a range of $10.80 to $49.20. 50 Superiority in calf 200d wt of top half of R 3yr heifers 40 superiority 30 20 10 0
9 Repeatability Repeat records from the same cows were only available from s that recorded all cows and were not available obviously from s that only recorded heifers. Data from the two commercial s with records from three years were used to estimate the repeatability of various measures. Even after editing the data to remove obvious outliers repeatability estimates of 200d wt and $ calf value per unit of NE varied widely. Correlations between years for s with multi-year records from different age cows cows calves years ages n CD cow wt BCS BCS5 wt BCS5MCW b wt wn wt 200d wt $ / NE G 2006/07 3, 4, 5 2007/08 3, 4, 5 6 6 0.23 0.68 1.00 0.96 0.34 0.71 0.87 0.80 0.81 0.81 * * 0.66 0.50-0.25 0.90 0.66 0.93 2006/08 3, 4, 5 6 0.03 0.97 0.09 0.68 0.68 * 0.32-0.09 0.69 2006/07 4, 5, >5 7 0.71 0.94 0.73 0.88 0.88 * 0.57-0.01 0.09 2007/08 4, 5, >5 7-0.03 0.94 0.66 0.65 0.65 * 0.77 0.69 0.84 2006/08 4, 5, >5 7 0.57 0.95 0.66 0.81 0.81 * 0.53-0.09-0.31 2006/07 2, 3, 4 13-0.22 0.95 0.57 0.94 0.94 * 0.36 0.47 0.17 2007/08 2, 3, 4 13 0.53 0.95 0.58 0.94 0.94 * 0.32 0.32 0.28 2006/08 2, 3, 4 13-0.45 0.92 0.18 0.91 0.91 * 0.22 0.05 0.08 2006/07 5, 5, 5 27 0.17 0.86 0.78 0.74 0.74 * 0.34 0.11 0.10 2007/08 5, 5, 5 27 0.19 0.89 0.68 0.71 0.71 * 0.66 0.17-0.02 2006/08 5, 5, 5 27 0.25 0.93 0.69 0.71 0.71 * 0.28 0.04 0.03 2006/07 all 67 0.16 0.92 0.76 0.77 0.28 * 0.48 0.38 0.30 2007/08 all 67 0.39 0.91 0.70 0.40 0.75 * 0.65 0.62 0.34 2006/08 all 67 0.18 0.90 0.63 0.76 0.72 * 0.25 0.12 0.12 B 2006/07>5, >5, > 48 0.34 0.51 0.40 0.47 0.47 0.46 0.29 0.07 0.04 2007/08>5, >5, > 27 0.00 0.37 0.35 0.13 0.13 0.13-0.30-0.27-0.13 2006/08>5, >5, >5-0.08 0.34 0.04 0.65 0.65 0.32 0.04 0.09 0.09 2006/07 all 112 0.13 0.80 0.22 0.79 0.45 0.43 0.49 0.40 0.44 2007/08 all 107 0.19 0.72 0.35 0.79 0.59 0.11 0.04-0.01 0.27 2006/08 all 69 0.08 0.65 0.04 0.79 0.61 0.25 0.30 0.38 0.40 C 2006-07 all 39 0.33 0.87 0.40 0.77 0.50 0.25 0.30 0.21 0.21 2006-07 5, 5 29 0.43 0.82 0.38 0.66 0.66 0.09 0.08-0.05 0.13 Data from the AgResearch at Whatawhata on the other hand produced much more consistent correlations between years. Adjustments for birth weight and gain to 200 days were calculated from the BINZ data and are given in Appendix 1.
Discussion 10 Techniques for measuring performance in extensively grazed beef s were applied to data from a number of commercial s. Variation in calf rearing ability and cow efficiency were found to be large both within s and between s. Estimates of the repeatability of both measures were widely variable when commercial data was used but when calculated from research farm data were less variable and more consistent with reports in the literature. There was no clear explanation why the repeatability estimates from commercial s varied so much and differed so much from those from the AgResearch. All of the farmers used electronic scales that presumably were accurate. Admittedly body condition scoring of cows is arbitrary and subject to personal variation. Perhaps the introduction of electronic tags will increase the accuracy of performance recording. Nevertheless moderate to strong relationships were demonstrated between repeat records of both 200d wt (calf rearing potential) and cow efficiency (calf potential per unit of net energy) which were high enough to suggest culling on previous records would increase efficiency of production. The effect of culling the bottom 10% of the main was modest for most s but the effect of culling the bottom 50% of each year s heifer crop was substantial. Selection of R 3yr heifers as main replacements based on the liveweight of the heifer as is currently practiced appears to be a particularly poor policy as there was little relationship found in this study. On the other hand the 200d weight of heifers calves appears to be a far more useful selection tool. Development of an automated performance recording database that would allow individual cow culling and benchmarking appears warranted and would increase the profitability of beef production from commercial properties. Adjustments for sex of calf and age of dam were calculated from the BINZ data using a linear model but were not used because of the relatively small numbers of records used to calculate them. Over two million calf records were used to calculate the BIO adjustments compared with only a few hundred for the BINZ adjustments. BINZ adjustments would be preferable once sufficient numbers become available because of differences in the breeds of cattle and farming environments. References Kress, D., & Burfening, P. (1972). Weaning Weight Related to Subsequent Most Probable Producing Ability in Hereford Cows. Journal of Animal Science, 35, 327-335. Lush, J. (1945). Animal Breeding Plans, Ames, Iowa: Iowa State University Press. National Research Council. (2000). Nutrient requirements of beef cattle.
Appendix 1 11 Beef Improvement Ontario additive adjustments birth wt gain to 200d sex of calf sex of calf AOD bull heifer AOD bull steer heifer 2 1.1 3.5 2 8.5 14.5 22.0 3-0.5 1.9 3-4.0 1.1 10.9 4-1.6 0.8 4-12.6-7.3 3.8 5-2.5 0.0 5-18.0-11.6 0.0 adjustments are to a 200 day old heifer calf out of a five year old cow Breedplan multiplicative adjustments Beef Improvement Federation additive adjustments AOD birth wt wn wt AOD birth wt wn wt male female 2 1.109 1.116 2 3.64 27.27 24.55 3 1.030 1.040 3 2.27 18.18 16.36 4 1.013 1.017 4 0.91 9.09 8.18 5 1.000 1.000 5-10 0.00 0.00 0.00 6 0.991 0.988 >10 1.36 9.09 8.18 8 0.985 0.980 10 0.993 0.990 12 1.018 1.020 to a 200d old calf out of a 5 year old cow calves of different sexes are treated calves of different sexes are treated as different contemporary groups as different contemporary groups Beef Improvement New Zealand additive adjustments birth weight gain to 200 days sex of calf sex of calf AOD bull heifer AOD bull heifer steer 2 3.8 5.7 2 15.1 28.9 20.1 3 0.3 2.2 3-2.7 11.1 2.3 4-1.0 0.8 4-10.9 2.9-5.9 5-1.9 0.0 5-13.8 0.0-8.7 adjustment is to a 200 day old heifer calf out of a five year old cow