Abstract:
Proc. Aust. Soc, Anim. Prod. Vol. 18 INTERRELATIONSHIPS BETWEEN PRODUCTIVITY AND FERTILITY IN DAIRY COWS J.B. MORAN* Eighty eight Friesian cows and heifers were fed one based on maize silage and containing increasing levels Days from calving to g DM/kg diet DM), in two trials. and to conception were recorded as were yields of In the live weight changes during early lactation. lactation data were recorded on all 46 animals. of four complete diets of grain (from 0 to 500 first observed oestrus milk and milk fat and second trial, complete Animals fed diets high in grain were more productive but required more Non-pregnant animals produced over 3 l/day more inseminations per conception. milk during early lactation and over 900 1 more milk (or 40 kg more milk fat) over the complete lactation than did pregnant animals. INTRODUC!l!ION The management of high yielding dairy cows must consider reproduction as well as nutrition, disease and milk harvesting. From surveys in the U.K., Esslemont (1979) concluded that maximum annual milk yields came from herds with calving However in intensively managed dairy intervals ranging from 330 to 360 days. A 35 herds, the mammary gland takes priority over the reproductive system. year survey in the U.S. clearly showed the negative association between milk yield and conception rate in lactating cows (Butler and Smith 1979). The threshold of herd productivity above which fertility is likely to be adversely affected would vary with the genetic makeup of the cow population. Esslemont (1979) cites Israeli studies suggesting this to be 8500 l/cow whereas In feedlot trials he suggests a more realistic level in Europe is 7000 l/cow. at Kyabram, Moran and Trigg (1989) and Moran (unpublished data) recorded lactation yields of up to 7600 1 fat corrected milk (FCM) or 350 kg milk fat Fertility observations made on these animals and their Per cow. interrelationships with productivity are reported below. XATERIALSANDHETHODS The Kyabram Friesian herd were upgraded over the last 20 years from a Jersey base and would be typical of many dairy herds in Victoria. Friesian heifers (in their first lactation) and cows (in their second or later lactations) were fed ad libitum in two trials on complete diets based on maize silage, lucerne hay I cottonseed meal, urea and minerals with increasing levels of grain (a mixture of rolled wheat and whole oats) in two trials during 1983 and 1984. Four diets were fed in each trial with grain levels increasing from 0 to 162 to 325 to 487 g DM/kg diet DM in Trial 1 and from 0 to 164 to 332 to 502 g DM/kg diet DM in Trial 2; these were designated Diets A,B, C and D with increasing grain level. Trial 1 involved 24 heifers and 18 cows fed from 45 to 101 days post-partum during autumn. Trial 2 involved 12 heifers and 34 cows fed from 48 to 146 days post-partum (early lactation) and for their complete lactation commencing in spring. Full details of diets, research methodology, together with dietary effects of production are presented by Moran and Trigg (1989). All 88 animals were artifically inseminated on the first heat after calving. The interval between calving and first observed oestrus was recorded-together with the number of inseminations per successful conception. For the 67 animals * Kyabram Research Institute, Kyabram, Vic. 3620. 300 Proc. Aust. Soc. Anim. Prod. Vol. 18 that conceived within 180 days post-partum, the time interval between first observed oestrus and conception was recorded. The data were analyzed using the GENSTAT statistical package (Numerical Three sets of analyses were conducted using linear Algorithms Group 1983). models which included the following factors: TR, PA, PR, trial, two levels for Trial 1 and 2. parity, two levels for heifers and cows. pregnancy status, two levels for pregnant and non-pregnant. The following continuous variables were also simultaneously regressed: GR, FY, LWC, BCC, grain content (%). milk fat yield during early lactation (kg/day). live weight change during early lactation (kg/day). body condition score change in Trial 2 (units/l4 weeks). The first analysis of fertility data was the following model: Y = a + b.TR + C-PA + d.PR + e.FY + g.LWC where Y was either time interval between calving and first observed oestrus or between first observed oestrus and conception (days). The second analysis of production data was the following model: Y= a + b.TR + C-PA + d.PR + e.GR + f.GR* + g.LWC + h.LWC x PA where Y was either yield of FCM or milk fat during early lactation (kg/day). The third analysis of production data in Trial 2 was the following: Y= a + b.PA + c.PR + d.GR + e.GR* + f.LWC + g.LWC x PA + h,BCC where Y was either yield of FCM or milk fat over the complete lactation (kg). For the three &snalyses, the partial regression coefficients (and standard errors) of levels of each factor and of each continuous variable were calculated. The significance of including factors and variables in consecutive order was determined by changes in the residual mean square in the corresponding analyses of variance. The final models only contained statistically significant (PXO.05) partial regression coefficients. RESULTS The two time intervals in the first model had normal distributions thus validating the least squares analyses carried out in the linear model. With the exception of TR, there were no significant effects of factors or variables on either days from calving to first oestrus or days from first oestrus to conception; average values (and standard errors) for Trials 1 v 2 were 30(23) v 42 (+3) days and 50 (25) v 77 (~4) days respectively. Animals fed Diets C and those fed Diets A and B per conception (1.9 v sieficant (P<O.O5). producing more than 290 conceive within 180 days D produced more milk fat during early lactation than (0.90 v 0.79 kg/day) but required more inseminations 1.3); both these differences were statistically It is of interest to note that of the seven-cows kg milk fat for their entire lactation, five failed to post-partum. 301 Proc. Aust. Soc. Anim, Prod. Vol. 18 The linear models for production during early lactation contained significant coefficients as follows: FCM yield: Y= 19.8 - 4.2(+0,9) PA + 0.30(+0.07) GR - 0.004(+0-001) GR* + 3.1(+1.0) PR - 4.6(+1.8) LWC r* = 0.48 r-8-d. = 3.6 Milk fat yield: Y = 0.83 - 0,17(+0,04) PA + 0.014(+0.003) GR -0.0002(+0.0001) GR* + 0,13(+0.04) PR - O-25(+0-08) LWC r* = 0.47 r-8-d. = 0.16 The linear models for production over complete lactations contained significant coefficients as follows: FCM yield: Y = 4983 - 714(+320) PA + 21(+7) GR + 913(+340) r 2 PR = 0.27 r-8-d. = 951 Milk fat yield: Y = 212 - 27(+14) PA + 0.9(+0.3) GR + 39(215) PR r* = 0.25 r-8-d. = 42 Table 1 presents the yields of cows and heifers in different status when fed the same diet (containing 240 g grain DM/kg diet the same live weight gain during early lactation (0.19 kg/day). cows produced 14% and non-pregnant heifers produced 17% more FCM during early lactation than their pregnant counterparts while values for complete lactation were 17% and 19% respectively. differences were statistically significant (PxO.05). Table 1 physiological DM) and with Non-pregnant and milk fat corresponding All these Predicted yields of fat corrected milk (FCM) and milk fat (with standard errors) in cows and heifers of different pregnancy status during early or complete lactations 302 Proc. Aust. Soc. Anim. Prod. Vol. 18 DISCUSSION Although productivity did not differ between trials, animals took longer to cycle and conceive in Trial 2. Calving intervals averaged 11.9 months in Trial 1 and 13.3 months in Trial 2. The lack of effect of milk fat yield on days to first heat is in agreement with Butler and Smith (1989) who noted the correlation between milk yield and days to first ovulation to be significant However they only after 40 days when most cows would have already ovulated. did conclude that high milk yields impair conception rates through delays or failure of early resumption of ovulation in the post-partum period. Production had an adverse effect on fertility (or vice versa) in that pregnant animals produced significantly less milk and milk fat and that high yielding Herd fertility is cows had lower conception rates at six months post-partum. influenced by current nutrition, cow condition, milk yield potential, current Because of these complex live weight change. milk yield and interrelationships, Esslemont (1979) noted that in only half of the studies cited, was there a significant association between yield and fertility. Furthermore, many of these interactions would have a threshold effect, hence would multiple regression analyses, which assume linear responses, For example, Ducker et al. (1985) underestimate their predictive values. reported conception rates in heifers to fall from 0.64 to 0.28 once they produced more than 20 1 milk/day. In a subsequent trial involving 24 lot fed cows yielding between 4200 and 7650 kg FCM (Moran unpublished data), of the five cows yielding more than 7000 kg FCM, or 320 kg milk milk fat, three failed to conceive within six months postMoate and Harris (1983) surveyed 1200 cows in Victoria, finding partum. conception rates to first services decreasing from 0.58 to 0.48 once their early lactation milk fat yields exceeded 1 kg/day. On the other hand, Fulkerson (1985) surveyed 2800 cows in Tasmania finding that less cows returned to service within 21 days as milk fat production increased up to 1 kg/day; above 1 kg/day, there was a decline in fertility. Clearly these cows were underfed in early lactation to such an extent that production and reproduction were both sub-optimal. Once feeding management during early lactation milk fat yields to approach 1 kg/day, it would should be placed on reproductive management. If nutritional demands later in lactation will be will not take place. In this study non-pregnant to 900 1 more FCM or 40 kg more milk fat over a pregnant herd mates. REFERENCES BUTLER, W.R. and SMITH, R-D, (1989). J. Dairy Sci, 72:767. DUCKER, M-J., HAGGETT, R-A., FISHER, W-J., MORANT, S-W. and BLOOMFIELD, (1985). Anim. Prod. 41:l. ESSLEMONT, R-J. (1979). In 'Feeding Strategy for the High Yielding Dairy Cow', p. 258, editors W.H. Broster and H. Swan. (Granada Press: London). FULKERSON, W.J. (1985). In 'The Challenge:Efficient Dairy Production', p.294, editor T.I. Phillips. (ASAP, Albury-Wodonga). MOATE, P. AND HARRIS, D. (1983). In 'Dairy Production Research Report', p-106. (Vi&. Dept. Agric. Rur. Aff.:Melbourne). MORAN, J-B. and TRIGG, T-E. (1989). Livest. Prod. Sci. 23: 275. NUMERICAL ALGORITHMS GROUP (1983). 'Genstat. A General Statistical Programme'. (Rothamstead Exp. Stn.: Harpenden). is improved sufficiently for appear that greater attention such animals fail to conceive, reduced as foetal development animals were found produce up complete lactation than their 303