Ian introduced this session outlining the content of his presentation – extremely broad as an overview of both work done in this space previously, but also up and coming new work. A causal web that draws associations between nutrition, cow genetics, environmental factors and nutrient demands including lactation and pregnancy is an excellent slide used by Ian to scene set the rest of the presentation.
Targets for the transition cows through calving were defined, and consequences of “short cuts” with transition management were discussed, for both NZ and offshore dairy animals. Plenty of good genetics in New Zealand but not matching that potential to express via appropriate feeding.
Best outcomes for reproduction based on heifer management and transition management. “No to sacrifice paddocks” and “Beets are not a balanced diet”, need appropriate convergence between agronomic and nutritional outcomes.
Better nutrition = reduced incidence of anoestrum cows, reduced periparturient disease in cows. A “typical” NZ diet that contains low levels of starch, CP in excess and fats that are high in conjugated linoleic acid (CLA) alpha linolenic acid ALA (18:3). In comparison, USA diets, feeding more total feed, starch high, CP low to Ok, fats low in 18:3. Production on average for USA will be 3x higher than for NZ cows.
Not in calf as an outcome. USA vs. NZ is discussed by Ian, a change where reproduction (not in calf) is improving in the USA.
Body condition score – standard stuff however the role for skinny and fat cows to fail reproductively remains typical, but of more concern for skinny than fats. Manipulating the BCS of cows is an important tool – particularly the bottom end of the herd, not just relying on “average” BCS for a herd.
The conundrum between cows that gain weight yet lose BCS. Tall cow vs short stumpy cows… same liveweight yet different labile body reserves. Ian has created a new metric that focuses on both weight and also BCS, resulting in six categories = middle, low, high BCS and middle, low, high on liveweight. This is impacted by parity – refer to the bar graph within Ian’s presentation for more detail.
Scott McDougalls’ early work / PhD around heifer BCS and anoestrus during the first lactation is referenced by Ian and the substantive delay in resumption of cyclicity if heifers are too light (BCS 4.5) vs. heavier heifers (BCS 6.5). Weight targets at 22 months of age must be met!!
LIC data is presented covering liveweight by age and breed category – data shows that heifers weights as % of adult weight are too light vs. target of 85% across all breeds. Motivation to achieve heifer liveweights – better repro, greater retention of best genetics and more milk from younger cows.
Cow longevity and risk of diseases such as milk fever, dystocia, RFMs, endometritis, displaced abomasum, ketosis, lameness, mastitis and respiratory disease. Older cows are more susceptible to reproductive failure with a delayed time to pregnancy, or fails to get in calf compared to young cows.
Milk production (at day 70) and probability of pregnancy – quadratic relationship (low and high producers more likely to fail), but this was also influenced by parity. Parity 1 cows had the greatest daily probability of pregnancy and parity > 5 had the lowest daily probability of pregnancy. In contrast, a dissimilar pattern was reported for pregnancy at first service.
The role for dietary fats explains much of the differences between reproductive success for USA and NZ cows. Primary role for fats is as an energy source and also as precursors for steroid hormones. Meta-analyses of fat vs. reproductive performance studies (67 total studies) demonstrated fat vs. probability of pregnancy, overall not significant. Limited value of meta-analysis due to few studies for each fat type, e.g. calcium soaps, tallow, CLAs (biggest response was to 18:2 CLA).
The benefits of fats in NZ pasture-fed cows, potentially beneficial particularly as rumen outflow rate is fast, therefore fats may bypass the rumen at arrive at small intestines unsaturated. Fats in pasture beneficial as are anti-inflammatory vs. maize silage fats are pro-inflammatory.
Ian provides an excellent quantitative illustration of the challenge of calcium loss and replenishment for periparturient cows and the roles for calcium. Further data demonstrates the impact of milk fever on disease and resumption of cycling and successful conception.
NZARN members a copy of the presentation is available below if you are logged in.
Non-members looking for more information are encouraged to use our ‘contact a nutritionist’ form and ‘member directory’ to find a member who can help them answer their questions.
If you are a Rural Professional interested in joining the NZARN please see our ‘membership’ section.
