First service to conception interval was six d ays longer for the H cows in the all age groups and in the three year & older group respectively; while in the two year old group, this interval was seven days longer for the H cows (Ta ble 3-5) . There were no sig nificant differences between H cows and L cows in the present study. The longer interval in the H cows reflected their lower conception rates to first service . The results in the present study agree with those reported by Garcia-Muniz, ( 1 998) H cows ( 1 7 days) and L cows ( 1 3 days) (Ta ble 3-9 ) . Also similar values were reported by Grosshans e t al., ( 1 997) a n d Macmil lan & Clayto n ,
( 1 980) 1 3 days and 1 1 d ays respectively.
The first service to co nception interval depends on the ability to conceive and maintain preg na ncy after a given service, and on the contin uation of ovarian cycles and the correct detection of oestrus in those cows, which do not conceive to initia l services ( Peters & Ball, 1 987) . A short FSC and CC are essential to maintain a concentrated ca lving pattern and a calving interval of 365 days in seasonal dairy herds ( Grosshans et. al. , 1 997) .
I ntervals between calving
For the estimation of calving interval in this study, calving dates for the m ultiparous cows were used o n ly. The H c ows had longer calving interval than the L cows (368 days and 365 days respectively) reflecting a higher i ncidence of inductions. H owever the results in the present study show a compact calving pattern com pared that reported by Garcia-Mu niz, ( 1 998) . Nevertheless, there were no differences betwee n the two strains.
1 42 Chapter 3
Macmillan e t al., ( 1 984) suggested that a more concentrated calving pattern should result in a higher submission rate and a higher conception rate simply because of a longer interval from calving to the next mating seaso n .
The role of live weight in reproductive performance
There c a n b e no doubt t h a t genetic im provement h a s indeed resulted in significa nt production a n d profit gains. However, the challenge is to keep that genetic potential but at the same time minimize the risk of negative effects on reproductive performance ( Verkerk, 2000°) .
Since 1 989 studies were initiated at Massey U niversity in order to validate the efficiency component of the breeding worth index of g e netic merit. The two herd lines have been bred using sires with d ifferent breeding values for live weight. The sires used for the heavy line had a hig her proportion of USA genetic background, which by 1 99 9 contained 28% of overseas Holstein-Friesia n genes compared to only 9% for the L cows. H eifers from the heavy line reached puberty 25 d ays later than those from the light line. Submission rates to AI were similar, but the conception rate to first service was 54% for the H cows
c o m pared to 65% in the L cows, which resu lted in a different
preg na ncy rate after 4 weeks of breeding of 58% a nd 70% for the H a n d L cows respectively ( H ol mes et a l ., 1 999) . Ta ble 3- 1 0 shows some vari a bles of lactation performance, live weight and body condition score for heifers .
Table 3- 1 0. Comparative performance of Holstein- Friesian cows bred for heavy (H) and light ( L) live weights at Massey University (from Garcia Muiiiz et al., 1 998; Holmes, et al., 1 999) Heavy Light Live weight (kg) : At birth ( kg) 40.7* 34.7* At first calving 4 1 1 * 386* Onset at puberty: Age (days) 325* 300* Live weight (kg) 24 1 220 % cycling at 1 2 months 83* 94* First lactation: Milk solids (kg) 278 277 Production efficiency (g MS/kg DM) 1 35 1 34
Calving to ovulation interval 28* 32*
Submission rate 2 1 days (%) 9 1 93
Conception rate to 1 st service (%) 54* 65*
*Significant difference ( P<0.05)
Reproductive performance
For many decades there has been a c o n cern that reproductive performance in the New Zea l a n d dairy herd is declining . Analysis of the national data base showed that the overall 2 1 -day su bmission rate ( S R ) decreased from 93.5% to 82. 1 % (from 1 973 to 1 996) , a rate of d ecrease of 0.5% per a n n u m , with an increase in the percentages of a noestrous cows in the herd , which bec a m e the major reproductive problem experienced in New Zealand ( Hol mes, 1 999; Verkerk, 2000°) . U n d o u bted ly, milk production levels have increased as a resu l t of genetic improvem ent so that feed req uirements of cows in early
lactation have a lso increased . Since a noestrus is largely a
consequence of failure to fu lly feed c ows, this is likely to be a contributing factor. Also average herd sizes have i ncreased which might contribute to less effective detectio n of heat a n d conseq u e n tly to less effective breeding. Therefore the reduced fertility of high genetic merit c ows has been recognised world wide, a n d fertility is n ow being included in the genetic index of several countries ( H o l mes,
1 44 Chapter 3
1 999) . Some evidence of the reproductive performance is presented in Ta ble 3- 1 1 . For instance conception rates have d ecreased by a bout 3% u nits per 1 0 years in USA, 6% units per 1 0 yea rs in Ireland, both in association with increased use of hig h genetic m erit cows with high increases in milk yield and protein .
Table 3 - 1 1 . Evidence of reproductive performance in different countries
Country Year Holstein- Jersey Source
Friesian
48-day non-return rate (%)
N Z 1 989 69 69 Burton & Harris, ( 1 999)
NZ 1 998 67 68 Burton & Harris, ( 1 999)
Submission rate (%)
NZ 1 973 94 94 Verkerk, (2000°)
NZ 1 996 82 89 Verkerk, (2000°)
Conception rate 1 st service (%)
USA 1 960 5 1 Lam ming et al., ( 1 998)
USA 1 980 46 Lamming et al., ( 1 998)
USA 1 995 40 Lam ming et al., ( 1 998)
IRELAN D 1 99 1 53 O ' Farrell & Crilly, ( 1 998)
IRELAN D 1 996 49 O ' Farrell & Crilly, ( 1 998)
Recent studies by
Kolver et al.,(2000) , have been evaluating the
performance of Holstein-Friesia n ( H F) cows with either 1 00% overseas (OS ) a ncestry or with less t h a n 1 2.5% overseas genes ( N ew Zealand selection lines) fed either total mixed ration (TMR) o r on high quality pasture at a generous allowa nce (>60 kg DM/cow/day) . I n this trial there were only a small n u m ber of a nimals incl uding 2 a nd 3 yea r olds. However calving dates were earlier in the NZ HF cows, a carry over effect of an unfavourable reproductive performance by the OS strain in the previous season . The reproductive performance of the OS strain differed from that of the NZ a nimals, with a trend to longer postpartum a noestrous intervals, for the pasture fed cows. Poor fertility reflects
reports from overseas studies in which repeat breeding is a c o m m o n reported problem, a nd wou l d a p pear t o be compounded b y factors related to the grass based diet, even tho u g h pasture' was fed at a generous allowa n c e . All these differences could be associated with the i n ability of the OS strain a nimals on pasture to maintain energ y
balance and b o d y condition score. presented in Table 3- 1 2.
Data from the study are
Table 3- 1 2. Reproductive performance of 2 and 3 year old cows during the 1 999/2000 lactation. ( Extracted from Verkerk et al., 2000b)
NZ os Significan ce
Reproductive performance: Grass TMR G rass TMR Grass TMR
Mean C alving date 24 July 29 July 1 9 Aug 10 Aug 0.05 NS Postpartum anoestrus interva l (days) 39 (6) 29 (4) 27 (6) 23 (2) NS 0.07
Calving to conception interval 74 (5) 72 (5) 6 6 (6) 70 (8) NS NS
Proportion empty after 1 3 week
1 / 1 4 2/ 1 4 5/ 1 3 3/ 1 4 0.08 NS breeding period
The proportion of OS H F genes in the NZ dairy herd has increased fro m 0. 7% i n 1 980 to 38% in 1 998. Harris & Win kelman, (2000) studied the influence of OS HF genetics o n NZ dairy cattle. This study involved 49.6% HF, 22.8% Jersey and 27.6% H F-Jersey cross cows. The reprod uctive performance of the predominantly OS H F gro u p was sig nificantly poorer than that of other breed grou ps, with particular concern a bout the lower c onception percentage (60.3%) to AI resu lting in a significant negative deviati o n of - 1 0. 1 % for the OS HF in c o n trast to the NZ H F grou p's deviation of + 1 . 1 % above average.
1 46
Chapter 3
T h e d ecrease in the 2 1 d ays s ubmission rate in N ew Zealand dairy h erds may be due in large part to underfeeding in early lactatio n that h a s occurred and despite the increased use of C I D Rs and inductions, i n the last decades, in order to maintain a compact calving pattern . Therefore, this problem will h a ve been accentuated by increased high g e n etic merit cows in the New Zea land herd, contri b u ting to increases i n t h e cow's energy dema nd and also increases in stocking rates. I n t u rn i t could b e t h e reasons for decreasing conception rate, b u t also the fact that more cows will n ow have to be mated a t their first post p a rt u m heat su bsequently expecting low conception rates.
The hig h empty rate could be reduced by increasing the use of i n d u ctions a nd C I D R s i n order to maintain a compact calving pattern, which is required in the New Zeala nd pastoral based dairy system . These will help t o achieve g ood fertility for the New Zealand conditions i n creasing the proportion of 3 weeks submission rates, a nd conception rated, while also maintaining a lower proportion of e m pty cows with o bvious less returns rates.
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