Uterine involution in the dairy cow : comparative study between organic and conventional dairy cows : a thesis presented in partial fulfilment of the requirements for degree of Masters of Science in Animal Science, Massey University, Palmerston North
Organic dairying is growing in popularity in New Zealand and the demand for
knowledge is ever increasing. Many more farmers are considering organics as an
alternative to their current conventional system. However, limited information is
available on organic dairying in a New Zealand pastoral situation particularly in
relation to its effect on fertility.
The New Zealand dairy industry requires the dairy cow to become pregnant every
year at the same time to maximise milk production and utilise the high pasture
production in spring. A cow requires 40 to 60 days for uterine involution to occur
and for resumption of oestrous cycles. It is critical that the cow becomes pregnant
within the six to eight week mating period, however, this can be difficult for late
calvers or those cows that had or still have a uterine infection, to undergo uterine
involution and be successfully mated. These cows will often not become pregnant
and as a consequence be culled for infertility.
During the first few weeks postpartum, the bacterial composition of the uterus
fluctuates as a result of spontaneous contamination, elimination and
recontamination. Most cows are able to eliminate these bacteria, however, 10 to
17% of cows are unable to do this. In these cows, the bacteria persist, cause
infection and inflammation, and delay uterine involution.
The main objective of this present study was to investigate the effect of different
management systems (Organic and Conventional) on productivity and
reproduction, particularly the process of uterine involution and its relationship with
reproductive outcomes. Uterine involution will be studied through the following
measurements: cervical diameter as assessed by measurement per rectum,
plasma concentrations of glucocorticoids and bacteriology of the uterus. Lactation
characteristics: milk yield, cumulative milk yield, milksolids production and somatic
cell count will also be investigated.
From the results, it can be concluded that Organic cows have reduced milk yield
(P=0.05) and milksolids production (P<0.01) through there were no major
differences at peak lactation or in the rate of decline after. However, overall
somatic cell count was not affected by management system though the
Conventional cows had high somatic cell counts in early lactation (P=0.925).
Cervical diameter was affected by the management system with the difference
between Organic and Conventional cows almost significant (P=0.06). Cortisol
concentrations were significantly higher in Organic cows (0.68 ± 0.08 ng/ml) when
compared to Conventional cows (0.95 ± 0.06 ng/ml) (P=0.01). Cortisol
concentrations decreased over time postpartum (P<0.01). Additionally Organic
cows had a shorter interval from calving to AI (P=0.017). However, none of the
other reproductive outcomes were affected by management system.
Simple correlations established that reproductive outcomes and bacterial counts,
reproductive outcomes and cortisol at Day seven, and cortisol and milk production
characteristics, were not independent of each other. Aerobic bacterial counts on
Day 28 and the interval from calving to AI were found to be significantly correlated
(r= 0.615). Stepwise partial regression analysis, plus analysis of variance
calculated on the relationships between uterine involution parameters and
reproductive outcomes found multiple weak correlations. It found that cervical
diameter, and aerobic and anaerobic bacterial counts on Day 28 were significantly
correlated with the interval from calving to first AI (P=0.018).
The differences in lactation characteristics are related to the lower pasture
production on the organic farmlet reducing the maximal potential milk production
and the possibly earlier calving dates of the Conventional cows. The differences in
bacterial counts and almost significant difference in cervical diameter may be
related to the lower cortisol levels and thus suggest that the Organic cows may be
less stressed. As stress suppresses the immune system, it may be possible that
the higher bacterial counts are indicitative of a less efficient or slightly weakened
immune system which takes longer to eliminate bacteria in the uterus; however this
is open to conjecture. The shorter interval from calving to AI suggests that Organic
cows may be exhibiting oestrus behaviour earlier postpartum or the Conventional
cows are having “silent heats” but this difference is possibly related to human
factors. The correlation between parameters of uterine involution and interval from
calving to AI, and the lower values for uterine involution parameters in Organic
cows suggest the possibility of faster uterine involution and this may result in better
fertility in the Organic cows. More research needs to be carried out to further
investigate the effect of organic dairying on uterine involution and reproduction
outcomes but organic dairying at the very least does not negatively impact on
uterine involution and fertility.