The effect of strain of Holstein Friesian cow and daily Cows were inseminated using AI over a 13 week feeding system on postpartum ovarian function milk by po6734

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									The effect of strain of Holstein-Friesian cow and                         daily. Cows were inseminated, using AI, over a 13 week
feeding system on postpartum ovarian function, milk                       period, starting in late April. Ultrasonographic
production and pregnancy rate to first service.                           pregnancy examination was conducted at 28-35 days
                                                                          post AI. Data handling was carried out using Microsoft
B. Horan1, 2, J.F. Mee1, P. Dillon1, P. O’ Connor1 and M                  Access 1997. Differences between strain of HF and FS
Rath2                                                                     were analysed using PROC GLM of SAS with a model
1
  Teagasc, Dairy Production Research Centre,                              containing the effect of strain, FS, lactation number and
Moorepark, Fermoy, Co. Cork. 2 Faculty of                                 their interactions. Chi-square analyses were used to
Agriculture, UCD.                                                         identify differences in pregnancy rate to first AI.

Introduction                                                              Results and Discussion
Genetic improvement within the Holstein- Friesian (HF)                    Neither FS nor strain of HF X FS affected any of the
breed for increased milk yield has resulted in reduced                    variables in Table 1. Strain of HF had no significant
cow fertility (Pryce and Veerkamp, 2001). A component                     effect on CLA. The mean interval to CLA was 31.5
of this reduced fertility may be due to the delayed onset                 days (s.e. 1.18), ranging from 6 to 100 days. The HD
and altered pattern of luteal activity. Many studies                      (62%) and NZ (57%) strains had a higher (P>0.05)
suggest that early commencement of luteal activity                        pregnancy to first service than the HP strain (40%).
(CLA), measured using progesterone profiles, is an                        Retrospective analysis categorising all cows into four
important pre-requisite to high fertility. The objective of               quartiles based on interval to CLA (<20 days, 20 to 26
the current study was to determine the influence of                       days, 27 to 44 days and >44 days), showed that cows
strain of HF cow and pasture based feeding system (FS)                    with longest and shortest CLA interval had
on early re-establishment of ovarian activity and                         significantly longer calving to conception interval than
subsequent pregnancy rate to first service.                               cows in the other two quartiles. Cows displaying
                                                                          abnormal progesterone profiles (38.4%) had similar 24-
Materials and Methods                                                     day submission rates, pregnancy rates to first service
Three strains of HF cows were compared: high                              and calving to conception intervals than cows classified
production North American (HP), high durability North                     with normal profiles. There was no significant
American (HD) and New Zealand (NZ). The HP strain                         difference in CLA, CLA to first AI interval or
were chosen on the basis of superior pedigree index for                   incidence of abnormal hormonal profiles between cows
milk production, while the HD strain were selected on                     pregnant or not pregnant to first service.
the basis of superior milk production, fertility and linear
(muscularity) traits. The NZ strain was selected using                    Conclusions
the highest possible genetic merit expressed in the New                   In the present study differences in pregnancy rate to first
Zealand genetic evaluation system (Breeding Worth),                       service between the HP strain and both the HD and NZ
with a minimum of 87.5% New Zealand Holstein-                             strains could not be attributed to differences in
Friesian genetics. Each strain was allocated to one of                    endocrine     parameters     monitored     using     milk
three FS: high milk output per cow from pasture (MP),                     progesterone profiling. Similarly, there was no
high concentrate feeding system at pasture (HC), and                      difference in endocrine parameters for cows that were
high milk output per unit area from pasture (HS).                         pregnant or non-pregnant to first service. This data set
Concentrate supplementation averaged 368, 364 and                         does not support the hypothesis that selection based on
1452 kg per cow for feeding system MP, HS and HC,                         CLA will improve pregnancy rate to first service.
respectively. Milk yield was recorded on five
consecutive days per week, live-weights weekly and                        References
body condition score every 3 weeks. Milk samples,                         Pryce, J.E. and Veerkamp, R.F. (2001) BSAS
representative of the whole milking, were collected                       Publication 26 (I): 237 – 249.
thrice weekly on Mondays, Wednesdays and Fridays                          Royal M D, Darwash A O, Flint, A F P, Webb, R,
during morning milking for progesterone profiling.                        Woolliams J A, Lamming G E Anim. Sci. 2000: 70:
Sampling began 5 days post partum and continued until                     487-501.
24 days after first AI. Endocrine parameter definitions                   Statistical Analysis Systems Institute. 2001.
were calculated based on the work of Royal et al.                         Cary, NC, USA
(2000). Oestrous detection was carried out four times

     Table 1. The effect of strain of Holstein-Friesian cow on ovarian function, animal production and pregnancy rate to first AI.
                                                                          Strain of Holstein Friesian                    SEM         P. value
                                                                   HP                HD                    NZ
 Number of cows                                                    39                  39                  39
 Commencement of luteal activity (CLA)(days)                      33.6                34.2                37.7            2.32         NS
 First inter-ovulatory interval (days)                            21.7                22.3                20.1            1.03         NS
 Atypical hormonal patterns (%)                                    39                  34                  42                          NS
 Calving to first oestrus (days)                                  43.8                43.3                42.0            2.24         NS
 Anoestrous cows (%)                                              10.3                 9.0                 6.4                         NS
 Milk yield at first AI (kg/cow/day)                              30.3a               28.7b               25.2c           0.57         ***
 Milk protein content at first AI (g/kg)                          32.3a               33.1b               34.3c           0.03         ***
 First service pregnancy rate (%)                                  40a                 62b                 57b                          *
                                                      abc
     NS = Non-significant, *=P 0.05, ***= P 0.001           values in the same row not sharing a common superscript are significantly different.

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