Online animal nutrition questions answered

Teagasc recently held their first live online questions-and-answers session on animal nutrition, through their corporate Facebook and Twitter accounts.

Nutrition specialist, Dr Siobhan Kavanagh, answered the questions.

Questions were received from dairy, beef and sheep farmers.

nWhat’s the best way to help avoid lazy cows during calving (cows on silage and half a kg of straw, pre-calver minerals)?

>> This sounds like it could be a sub-clinical milk-fever problem. This can be caused by over-fat cows; excessive potassium levels in silage (a lot of slurry going on silage ground); inadequate magnesium supplementation (your pre-calver is probably supplying 15g of magnesium. I would feed an additional 30 grams of sweetened calmag with your pre-calver mineral).

*How do you rate seaweed as a natural mineral supplement?

>>When feeding any mineral mix, it’s important to know what minerals are needed by the animal, and ensure that the mineral mix used is meeting the animal’s requirements.

Seaweed minerals tend to be high in iodine, but it’s important that the requirements of the animal, for other minerals, are also met in the mix. I would be more concerned about individual mineral inclusion in the mix (major and trace elements, selenium, iodine, etc) rather than the source of a mineral.

*What is the best-value fodder or meal to buy to extend dry cow feed, if silage is running low?

>>65 DMD silage is worth approximately €25-28 per bale, when meals are approximately €320/tonne, but the problem is that silage is often of unknown quality.

I would be slow to make major changes to the cow’s diet in the last few weeks pre-calving, so changing those from full silage to restricted silage and meals is not ideal. But, certainly, the late-calving cows could be put on restricted silage and meals. If you are 25% short of the silage you need, that’s about 2kg of meals. If you are short 50%, 3-4 kg of meals.

Consider, also, restricting the young stock on the farm, such as weanlings.

If you still have cull cows, its time to finish them, possibly on high meals.

You need adequate feeding space, if feeding restricted silage and meals.

>>

*If a bull is running with 40 sucklers, and I want to throw dairy nuts to the cows to prevent grass tetany and bring them into heat quicker, will the dairy nuts affect the bull’s libido in any way?

>>If the cows are at-grass, I would question the need to feed ration, unless they are being bred indoors on silage. It’s probably preferable that the bull is not eating the ration with a high level of magnesium in it, as it can cause urinary problems in males — urolithiasis, it’s basically a build-up of minerals (especially magnesium) in the urinary tract, which affects the passing of water. It’s a bigger issue if not consuming enough water. This may upset the bull, and possibly his libido, also.

*What are the most important minerals to feed a cow that is near calving?

>>The important minerals, pre-calving, for cow and calf health are: magnesium (important for milk fever), clinical and sub-clinical trace elements (copper, selenium, iodine, cobalt, zinc and manganese), and vitamins (particularly vitamin E).

*Considerable variation in RFI (residual feed intake) exists among individual animals within breeds or genetic strains. This variation suggests that substantial progress can be made in RFI, since the heritability of the trait is about 40%. What advice would Siobhan give on reducing RFI in bull beef finishing systems?

>>Yes, there is considerable variation in RFI, but the challenge is to reliably identify the efficient animals. [Measuring feed efficiency is very costly, hence all talk about markers for the trait].

There is a breed ranking for RFI, with late-maturing breeds being more efficient than early-maturing breeds. Theoretically, one can generate breeding values for RFI (but with low reliability), using Tully data and select/identify animals accordingly. Alternatively, one could try and identify/select animals on the basis of the individual sub-components of our breeding indexes — intake, weight, growth.

What makes RFI particularly useful is that it is independent of body size and production — that is, broadly, it quantifies the variation in feed intake that is unrelated to weight and growth. It’s important to remember that the main advantage of RFI over conventional measures of feed efficiency (FCR, FCE) is in the breeding herd; that is, you can select for feed-efficient animals without increasing mature size. [We are not advocating single-trait breeding selection, but the components of RFI can be incorporated into multiple trait selection programmes].

In finishing cattle of similar weight, practically FCR is probably as useful as RFI (phenotypically).


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