Effects of Early and Late Breeding of Heifers on Multiple Lactation Performance of Dairy Cows! 1

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1 Effects of Early and Late Breeding of Heifers on Multiple Lactation Performance of Dairy Cows! 1 C. Y. LIN, A. J. McALLISTER, T. R. BATRA, and A. J. LEE Animal Research Centre Agriculture Canada Ontario K1A 0C6 OC6 Canada G. L. ROY Lennoxvitfe Lennoxville Research Station Quebec J1M 1Z3 Canada J. A. VESELY Lethbridge Research Station Alberta T1Z 4B1 481 Canada J. M. WAUTHY Normandin Experimental Farm Quebec G0W GOW 2E0 2EO Canada K. A. WINTER Charlottetown Research Station Prince Edward Island CIA C1A 7M8 7MB Canada ABSTRACT Dairy heifers were randomly divided into two treatment groups. One group of 253 heifers was bred at first estrus after 350 d of age and the second group of 249 heifers after reaching 462 d of age. Feeding and management practices were identical; groups differed only in age at first breeding. This report compares production of second and third lactations, reproductive traits observed during first and second lactations, and lifetime performance. Comparisons of heifer reproduction and first lactation production were reported earlier. Although the 462-d breeding age group of heifers had slightly better first lactation performances than the 350-d breeding age group, these advantages were not carried over to second and third lactations. No significant differences existed in three-parity per per- reformance between the two breeding groups. The 350-d breeding group had longer 61-mo productive life (730 vs. 623 d), produced greater 61-mo total milk (10,693 vs kg), and yielded more Received December 2, Accepted April 29, Animal Research Centre Contribution No milk per day of 61-mo herdlife (6.8 vs. 5.9 kg). A reduction of 1 mo in age at first calving would increase three-parity and 61-mo total milk by 427 and 554 kg, respectively. Results from this study suggest that early breeding is a viable and practical approach to improve profitability for the dairy industry. INTRODUCTION Age at first breeding is important in affecting productive and reproductive performance of heifers in the first and subsequent lactations. The main advantages of breeding heifers at an early age are reduced rearing cost for heifers and earlier return of income from milk. However, the disadvantages are decreased milk yield in the first and subsequent lactations and increased risk of calving difficulties (1, 6, 8, 12, 15, 17, 18,19). 19). Most studies comparing different breeding ages in heifers were based on field data and not planned for that purpose (1, 7). The use of field data for assessing effects of heifer's breeding age is questionable because of the partial confounding of breeding age with growth and reproductive disorders. The decision to begin breeding heifers is often based on weight, body size, age, or some combinations of these factors. The few planned comparisons involved small numbers of animals (3, 5, 12, 1988 J Dairy Sci 71:

2 2736 LIN ET AL. 19). This experiment was designed to study effects of age at first breeding on subsequent growth, production, and reproduction for hei- heifers reared identically. Effects of early and late breeding on production and reproduction of heifers from this experiment were reported previously (11). Results from the first phase study suggest that heifers of the 350-d breeding group had lower milk yields at both 168 and 308 d of first lactation than those of the 462-d breeding group. The purpose of this second phase study was to compare these early and late bred heifers for both three-parity and 61-mo performances. MATERIALS AND METHODS Experimental Procedures This experiment was part of a dairy cattle breeding project of Agriculture Canada. Details of the design and the management procedures of the breeding project are described by McAllister et al. (13). The experiment involved five research stations of Agriculture Canada (Charlottetown, Prince Edward Island; Norman- Normandin, Quebec; Lennoxville, Quebec; Ottawa, Ontario; and Lethbridge, Alberta) and three lines of hei_':rs hei.'.:rs (Holstein-based H line, Ayrshire- Ayrshirebased A line, and C line crossbreds between the H and A lines). Two hundred fifty-three heifers were bred at first observed estrus af;-er 350 d of age (350-d breeding age group), and 249 heifers were bred at first observed estrus after 462 d of age (462-d breeding age group). Daughters of a sire were randomly assigned to the two breeding age groups. All heifers were born between October 1980 and December 1981 and were subject to similar feeding and management practices. The rearing program for the two groups differed only in age at first breeding. All females of both groups intermingled in each station during the course of the inter- experiment and had an opportunity to complete the third lactation when the analyses were carried out. Reproductive traits observed during first and second lactations were number of services per conception, conception rate at first service, days open, service period (number of days from first service to conception), gestation length (days from last service to calving), and calving interval. Also, age, calving ease, and placental condition at second and third calvings were evaluated. Cows were observed for estrus twice daily. Frozen semen in pellet form was used for all inseminations. Cows were bred at the first observed estrus following 55 d postpartum. Ease of calving was scored as normal or difficult. If the placenta was expelled within 24 h after calving, it was considered normal, otherwise retained. Cows open longer than 280 d post- postpartum were culled. Additional culling, primarily involuntary, was done without regard to the breeding age group for production, reproduc- reproduction, disease, injury and other causes. Milk yields were based on a single daily yield recorded weekly. Animals were dried off when daily yields of 2 consecutive wk dropped below 5 kg for first lactation heifers or below 9 kg for second and later lactation cows. Drying off occurred not less than 60 d prior to next parturition. Three-parity total milk was the sum of up to first three lactation yields during productive life. Total milk to a fixed age of 61 mo (i.e., 61-mo total milk) was computed. Three-parity (or 61-mo) yield per day of productive life was calculated as three-parity (or 61-mo) total yield divided by productive life. Similarly, three-parity (or 61-mo) yield per day of herdlife was calculated as three-parity (or 61-mo) total yield divided by the herdlife. Herdlife was defined as days from birth to disposal or to the end of third lactation, which- whichever occurred first. Likewise, productive life was defined as days from first parturition to disposal or to the end of third lactation. For 61-mo 61-too performance, herdlife was defined as days from birth to disposal or to 61-mo of age while productive life was defined as days from first parturition to disposal or to 61 mo of age. All animals had the opportunity to complete up to three lactations and to survive up to 61 mo of age. Milk yields are not adjusted to a mature equivalent basis. Yield for the entire lactation was included in the analyses regardless of length. Body measurements were body weights (kg), withers height (cm) and heart girth (em) (cm) at calving, weight loss of the cow from calving to 112 d postpartum, and birth weight of the calf. Only birth weights of live calves were recorded. Statistical Analyses The model for the analysis of three-parity total yield, 61-mo total yield, yield per day of productive life, yield per day of herdlife, and

3 EFFECTS OF EARLY BREEDING 2737 reproductive traits includes the effects of station, year of birth, 3-mo calendar season of birth, line, breeding age group, line by breeding age group and station by breeding age group interactions, and error. Birth weight of the calf and second and third lactation yields were analyzed by a model that included the effects of year of freshening, season of freshening, station, line, breeding age group, line by breeding age group and station by breedi:lg breeding age group interactions, and error. All effects in both models were considered fixed except for error term and a least squares analysis of variance was used. Effect of sire was not included in any analyses because the daughters of a sire were randomly assigned to the two breeding age groups. Intraclass regressions of three-parity and 61-mo total yields on age at first calving were fitted for the two breeding age groups in one analysis and the overall regression (the same regression slope for both breeding age groups) in a separate analysis. The number of observations differed for traits measured about the same time in a cow's life because of invalid or unrecorded data or early postpartum culling. RESULTS AND DISCUSSION Body Measurements Least squares means and SE for body measurements are in Table 1. The 462-d breed breed- breeding group had greater (P<.Ol) (P<.01) body weight (550 vs. 516 kg), withers height (131.2 vs cm), and heart girth (190.3 vs cm) than the 350-d breeding group at second calving. The significant differences in these measurements at second calving likely resulted from the differences in calving age (38.4 mo for 462-d group vs mo for 350-d group). Late bred heifers lost more (P<.05) body weight (15.9 kg) from second calving to 112 after second calving than early bred heifers (5.4 kg). Late bred heifers lost more weight at second calving mainly because greater fat catabolism was required to support higher milk production. There were no significant d~"ferences d:. ferences in body measurements at third calving between the two groups with the exception of 112-d weight postpartum of third lactation. Weight loss from third calving to 112 d postpartum was not significantly different for the two groups. Weight loss was greater at third lactation than at second lactation for both differ- breeding groups, presumably because both groups produced greater milk yield in third lactation than in second lactation. Although significant difference in birth weight of the calf existed between the two breeding groups in first parity (11), there was no significant differences in second and third parities. Calving Ease and Placental Condition Of 160 second calvings for 350-d breeding group, incidences of calving difficulty and retained placenta were 5.6 and 9.4%, respectively (Table 2).The 462-d breeding group had 154 second calvings of which incidence of calving difficulty was 9.7% and that of retained placenta was 10.4%. The differences in incidences of calving difficulty and retained placenta between both breeding groups were not statistically significant. Results were similar for third parity. Although calving difficulty in first parity has been associated with early breeding (12, 18, 19), results from this study and our first parity results (11) suggest no significant difference in calving difficulty between the two breeding groups for the first three parturitions. Amir and Halevi (2) reported no significant differences in calving difficulties for first parturition among different calving ages ranging from 20 to 25 mo of age. The differences of 3 mo in ages at second and third calvings between the two groups (Table 3) might not be large enough to influence significantly calving ease. Difficult calvings usually occur more frequently among heifers than among cows. For second and third calvings the influence of calving age on frequency of calving difficulty is less critical. differ- Reproductive Performance Mean age at second calving was 35.2 mo for 350-d breeding group and 38.4 mo for 462-d breeding group. Mean age at third calving was 48.2 mo for 350-d breeding group as compared to 51.5 mo for 462-d breeding group. These differences were significant (P<.Ol). (P<.01). There were no significant differences between both breeding groups in service period, days open, first service conception rate, number of services per conception, and gestation length observed during first and second lactations (Table 3). Amir and Halevi (2) reported no significant differences in days open and the number of days from first insemination to conception

4 ' o c:: e"..., ::J E Ọ.., Q o "~. Vl ct~ 1'1 n' W ~ TABLE Least squares means and SE for body weights and measurements by breeding age group. " <~ < "... Z zo... o... '0 co co Breeding age group 350 d 462 d Significance' n X SE n X SE Second parity Body weight at calving, kg d l12-d Weight postpartum, kg Weight loss from calving to 112 d postpartum, kg Birth weight of the calf, kg t""" Withers height at calving, cm Z Heart girth at calving, cm ṃ.,,q Third parity ~ > t""" Body weight at calving, kg 112-d Weight postpartum, kg Weight loss from calving to 112 d postpartum, kg Birth weight of the calf, kg Withers height at calving, cm Heart girth at calving, cm , 1 Difference bl'tween between the two breeding groups. P<.05. *P<.05. * P<.01. *P<.01. Nha "-I "-4 w 00

5 EFFECTS OF EARLY BREEDING 2739 TABLE 2. Calving ease and placental condition by breeding age group. Breeding age group 350 d 462 d Significance Second parity No. calving Difficult calving, % Retained placenta, % Third parity No. calving Difficult calving, % Retained placenta, % between different calving age groups. Both groups had similar lengths in first and second calving intervals. However, second calving interval was longer than first calving interval (394.4 vs d for 350-d breeding group and vs d for 462-d breeding group). This observation is understandable since older cows have longer gestation periods (16) and more days open (4) than first-calf heifers. Second and Third Lactation Yields The two breecing breeding groups were similar in milk yield and the number of days in milk during second and third lactations (Table 4). The 350-d breeding group produced 19.3 kg milk/d during second lactation, which was significantly less than 20.7 kg for the 462-d breeding group. Milk per day during third lactation did not differ significantly between the two breeding groups. Although age at first breeding is an important factor affecting first lactation yields in this experiment (11), its impact on second and third lactations was negligible. These results clearly indicate that the effects of age at first breeding on lactational performances decrease with increasing number of lactations. Three-Parity Lifetime Performance Three-parity lifetime performance up to and including the third parities is in Table 5. There were no significant differences between breeding age groups in herdlife, productive life, total milk, total milk per herdlife, and total milk per productive life. Bettenay (3) reported that first matings at either 12, 15, 18, or 24 mo of ages had significant effects on total milk production of first four lactations based on 43 cows with complete information for four lactations. Comparing survivors of the four lactations among the different breeding age groups obviously favors the late breeding group, because age effects on milk yield are greater than effects of parity. Effect of breeding ages on total lifetime milk based on survivors only is particularly notable as there was a 12-mo difference in breeding age between the earliest and the latest breeding age groups in Bettenay's study (3) compared with 112 d (about 3.7 mo) difference between the two breeding age groups in this study. 61-Month Lifetime Performance Total performance up to 61 mo rna of age is summarized in Table 5. The two breeding age groups did not differ significantly in herdlife or total milk per productive life. However, produc- productive life from first calving up to 61 mo rna of age in life was longer (P<.05) for 350-d breeding age group than for the 462-d breeding age group (730 vs. 623 d). Concomitantly, 350-d breeding age group produced greater (P=.07) total milk accumulated up to 61 mo rna of age in life than the 462-d counterpart (10,693 vs kg). In this connection, Amir and Halevi (2) reported that accumulated milk yields up to 41 mo rna of age were greater for heifers calving at 21 mo rna of age than those calving at 22, 23, or 24 mo rna of ages. Lin and Allaire (10) found that selection on total milk produced up to 41 mo rna of age was more efficient than selec- selection on milk produced to 305 d in first lacta- lactation for genetic improvement of total milk produced up to 48 mo, rna, 72 mo, rna, or for the cow's lifetime, respectively.

6 ' o... '" e- ::I ~ ọ.., o e:. NtJ ---l -I'- o -<[Jl ne~ ;;. ::I n '"-< < ~..., ~q... z o ~ ' TABLE Least squares means for reproduction traits by breeding age group. Breeding age group 350 d 462 d Significance' I n X SE n X SE n X SE n X SE Reproduction during first lactation: : Service period, d Days open First service conception rate, % No. of services per conception r- Gestation length, d t" Z Reproduction during second lactation: ttl Service period, d , ,4 -l Days open ,0 8.2 > r First service conception, % No. of services p.er conception Gestation length, d ,1 1.5 Age at second calving, mo ** Age at third calving, rno mo ** First calving interval, interval, d Second calving interval, d , 1 Difference between the two breeding groups. P<.01. **P<.01.

7 EFFECTS OF EARLY BREEDING 2741 TABLE 4. Least squares means for second and third lactation performance by breeding age group. Breeding age group 350 d 462 d Significance11 X" X SE R X SE Second lactation: No. cows Milk yield, kg Days in milk Milk per day in milk * Third lactation: No. cows Milk yield, kg Days in milk Milk per day in milk Difference between the two breeding groups. *P<.05. The 61-mo total milk was greater than the three-parity total milk in the 350-d breeding group. This means that 61 mo of age has occurred during the fourth lactation for some of the cows. Milk produced per day of herdlife (total milk/herdlife) for the 350-d breeding age group was 6.8 kg, which was greater (P<.05) than 5.9 kg for the 462-d breeding age group. This is so because the 350-d group produced greater 61-mo total milk than the 462-d breeding group while 61-mo herdlife was about the same for the two breeding age groups (Table 5). Although not statistically significant, milk produced per day of productive life (total milk/productive life) was slightly higher for the 462-d breeding age group than for the 350-d TABLE 5. Least squares means and SE for lifetime performance by breeding age group. Breeding age group 1i 350 d 462 d Significance' 2 X.X SE X SE Three-parity lifetime performance: Herdlife, d 1, , Productive life, d Total milk, kg 10, , Total milk/herdlife Total milk/productive life mo Lifetime performance: Herdlife, d 1, , Productive life, d * Total milk, kg 10, , t Total milk/herdlife Total milk/productive life Number of cows is 215 for 350-d breeding group and 223 for 462-d breeding group., 2 Difference between the two breeding groups. *P<.05. t-i-p p =.07.

8 2742 LIN ET AL. breeding age group (15.1 vs kg). This results primarily from shorter productive life in the 462-d breeding age group because productive life was used as a denominator in calculating total milk/productive life. Large within-group variation in lifetime production existed in these data since all records initiated were included in analyses. This reduced the sensitivity of tests of significance. Productive life and herdlife are two com- commonly used measures of stayability in dairy cattle. Although productive life is a part of herdlife, it is a more meaningful measure of stayability because dairy farmers are more concerned with how long a cow remains produc- productive in her lifetime than with how long she stays in the herd regardless of the length of productive life. The two breeding age groups showed significant difference in productive life but not in herdlife, suggesting that early breeding did not reduce stayability. Our results suggest that concern that heifers bred at an earlier age could have detrimental physiological effects resulting in reduced herdlife is not warranted. As such, the advantage of early breeding over late breeding in total milk up to 61 mo of age in life would increase with increasing differences in age at first calving between the breeding groups. Similar mean herdlife herdiife up to 61 mo of age (1430 vs d) and body size (Table 1) for the two breeding groups suggests that both groups of cows consumed similar amounts of feed for basic body maintenance up to 61 mo of age and required similar fixed cost to maintain. However, total milk to 61 rna mo of age was significantly (P =.07) greater for the 350-d breeding group than for the 462-d breeding group. These results suggest that the primary economic benefits of early breeding are an increased gross revenue per unit of time and an earlier return on investment. However, current heifer rearing programs used in the dairy industry are geared toward a later breeding age than is that of 350-d breeding group. Proper modification of rearing programs may be required to accommodate early breeding practice in order to reap maximum benefit from it. Relation Between First Calving Age and Lifetime Performance main- Linear and curvilinear curvitinear regressions of total yields on age at first calving (adjusted for fixed effects of breed, station, year of birth, season of birth, breeding age group, and interactions of breeding age group with station and breed) were examined in separate analyses. Linear regressions of three-parity or 61-mo total milk on first calving age were significant (P<.01), whereas the curvilinear regressions were non- nonsignificant. The two breeding age groups did not differ in linear regression coefficients of three-parity or 61-mo total milk on first calving age. One-month reduction in first calving age would increase three-parity total milk by 427 kg and 61-mo total milk by 554 kg. Apparently, age at first calving affects 61-mo total milk more than three-parity total milk. Similarly, Lin and Allaire (9) estimated that a 1-mo decrease in age at first calving was equivalent to an increase of 471 kg milk in computing total profit up to 72 mo of age. Their study also indicated that age at first calving was the most important variable, next to milk yield, for improving lifetime profitability or profit from birth to 72 mo of age. Gill and Allaire (7) reported that optimum age at first calving for total lifetime performance was 23 mo, which is the mean age at first calving in the 350-d breeding group. In contrast, mean ages at first calving were 28.8 mo for Ayrshires and 27.5 mo for Holsteins in the US dairy industry (14). CONCLUSIO The age at which a heifer is bred to calve for the first time has important effects on first lactation productive and reproductive performances. Its impact on subsequent lactations decreases with increasing number of parities. The early breeding age group had greater (P =.07) total milk up to 61 mo of age when compared with that of the late breeding age group. Furthermore, the results indicated that early breeding would not cause cows to be adversely affected in lifetime performance. Thus, it makes good economic sense for the dairy industry to practice early breeding at 12 to 13 mo of age coupled with a proper heifer rearing program, since early breeding would generate more income from milk sales at a fixed age in a cow's life. perform- ACKNOWLEDGMENTS The authors gratefully acknowledge operational and technical staff at all stations for care of the animals and collection of data. opera- Journal of Dairy Science Vol , No. 10, 1988

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