How to achieve maximum fertility levels through your cow’s diet

Welcome to the first addition of our Nutrition Series, a six-part video and article series brought to you by Dairygold and Alltech Ireland for the next six weeks.

Liam Stack, M.Agr.Sc Dairygold Ruminant Technical Manager

As cows approach the breeding season, they need to be on a rising plane of nutrition in order to ensure maximum fertility levels for bulling.

Signs that your cows are NOT on a rising plane of nutrition

– Low milk proteins

– A milk butterfat to protein ratio of greater than 1.4:1

– Excessive BCS loss: a body condition score loss of greater than 0.5 in the 8 weeks after calving

How to meet your cow’s energy demand

1. Feed an appropriate level of concentrates based on how much grass your cows are consuming, your herds milk yield and your grass supply
2. Do not over estimate grass intakes. Over estimating grass intake by 1kg dry matter is the same as lower concentrate feeding rate by 1kg daily
3. If your cows current BCS is less than 2.75 you can

• feed 1 kg extra concentrates compared to the standard feeding advise
• Put these cows on once a day milking while holding concentrate feeding levels. This will negatively affect milk yield while improving BCS

Concentrates required: Grass + concentrates

*grass alone does not meet a cow’s daily requirement for calcium, phosphorus, magnesium, zinc, iodine and selenium. Even though a cow’s energy demand might not require concentrates, feeding 1.5kg of concentrates at grass is the cheapest and most effective method of supplying these minerals.

Mineral Nutrition:

Grass does not meet your cow’s Phosphorus, Calcium, Selenium, Iodine, Zinc requirements. Cows also need a daily intake of Cal Mag to prevent grass tetany.

Dietary deficiencies of copper, selenium and iodine are linked to:

– poor fertility,

– cystic ovaries,

– anestrous,

– irregular or suppressed oestrus

– and early embryonic death.

Grass Tetany:

Grass tetany is caused by a lack of magnesium (Mg) absorption. Grass tetany affects muscle function, hence the trembling/twitching/trashing. Death is caused by the heart (a muscle) giving up.

Factors causing grass tetany:

1. Not feeding magnesium: Magnesium is not stored by the cow. Daily supplementation is required.
2. Anything that affects intake: Bad weather, stress, poor grass covers, cows in heat
3. Decreased rumen function. Magnesium is absorbed by the cow in the rumen. Lush highly digestible grass passes through the rumen quicker than lower digestibility forages. The cow has less of a chance to absorb the magnesium. Magnesium is stored in the grasses stem. Lush covers have a higher leaf to stem ratio and therefore a lower magnesium content.
4. High grass potassium decreases magnesium absorption, have you spread a lot of 18-6-12 this spring?
5. High grass Nitrogen. High levels of ammonia breakdown in the rumen decreases magnesium absorption
6. Low sodium (Na) content decreases magnesium absorption
7. Milk yield. Higher yielding cows need more daily magnesium