Nutritional effects on heifer productivity

Results:

Heifers fed the low protein diet (10% crude protein (CP)) showed faster rates of growth during mid and late pregnancy than heifers fed the high protein ration (18%CP) before the breeding period. This was associated with an increase in body condition score (BCS) and significantly increased calf birthweight (3kg) which resulted in more assisted calvings within this group.

Diet fed prior to calving had significant effects upon the time taken for the heifer to re-breed. Heifers which lost body condition prior to calving resulted in low levels of the hormones leptin and progesterone being produced which are required to enable the cow to restart cycling post-calving. Heifers continued to lose weight until 3 months after calving and did not regain pre-calving weight until 5 months post calving. This resulted in an extended post-partum interval and a delay in getting back in calf during the following breeding season.

The study found that suckling behaviour was increased in calves from dams fed low protein, however this had no effect on calf growth rate. Overall, protein level fed pre-or-post conception had no effect on the performance or future breeding success of the heifer’s offspring.

Heifers fed a 14.5%CP (in DM) ration compared to a 10.4%CP ration had greater numbers of follicles in the ovary and also higher concentrations of circulating progesterone. Progesterone plays an important role in embryo survival indicating that protein supplementation may be required to maximise fertility in beef heifers if dietary protein level is below 14%CP.

Conclusions:

• Nutrient intake prior to conception and during early gestation may increase calving difficulties in beef heifers calving at 2 years of age when combined with altered diet in mid and late gestation
• Heifers must calve at a BCS 3 if they are to restart cycling and conceive within 85 days after calving
• Milk intake of the calf may be increased by a low protein diet in early gestation which may result in increased growth rates
• Protein supplementation may be beneficial in maximising fertility in young beef heifers if the dietary protein intake is below 14% CP
• Protein level fed pre-or-post conception had no effect on the performance or future breeding success of the heifers offspring
• Planned activity

The results will be used to produce a number of articles and a number of on-farm events have already been delivered to the industry as part of this project.

The Problem:

Current nutritional advice to beef farmers is in need of updating to reflect the improved genetic base of the national suckler hard and the shift in the breeds used as suckler females. It is now recognised that nutrition during pregnancy can have long term consequences on not only the dam but their progeny as well. This study will focus on the role of nutrition during pregnancy and its consequences on ease of calving and lifetime productivity of suckler heifers.

Aims and Objectives:

Aims

• Determination of the effect of nutrient intake during early-gestation on the occurrence of dystocia in nulliparous beef heifer calving at 2 years of age
• Assessment of the usefulness and ease of pelvic area measurement in these heifers as an aid to minimise the risk of dystocia resulting from the nutritional regimes imposed and investigation of the association between maternal hormones, indicative of placental functional capacity and metabolites, to be used as indicators of fetal well-being and of dietary supplementation requirements
• Determination of milk intake of the calf during the first 6 months of life and growth rates to 12 months of age
• Assessment of effects upon calving to conception interval and effects upon reproductive organ development and development of following offspring

Deliverables

1. Tools for providing clear nutritional advice to farmers and vets: The provision of this robust data set will enable the development of tools (via assessment of suitable blood metabolites or hormones) that provide clear evidence of nutritional well- being or requirement, to both the pre-mating and the pregnant heifer and effects on calving ease
2. How nutrition can meet the challenge of reducing greenhouse gas emissions: We will deliver data on how to increase productivity by increasing the kg of beef produced per ha which will reduce the greenhouse gas emission per animal. The project is also focussed around the grass production system
3. The Low carbon farm: Increased efficiency of production per animal decreases the carbon footprint. This research on the effect of in utero protein on birth weight, milk intake, calf growth, reproductive performance, and carcass traits on the current and a subsequent generation is essential to this increased efficiency

Approach:

Two groups of heifers will be randomly allocated to a high (H;21% crude protein) or low (L11% crude protein) protein diet from 60 days prior to conception. These 2 dietary regimes reflect the normal range of protein intake of cattle out to pasture. Heifers will be mated to a single bull with known EBVs using AI after synchronisation. Then half of the heifers will be switched to a high or low protein diet at turn out 18 days after conception i.e. coincident with uterine attachment, thus giving 4 nutritional groups i.e. HH, HL, LL, LH (n=12 /group).

All animals will undergo, blood collection for hormone and metabolite analysis each month from initiation of trial and, ultrasound scanning to determine fetal growth, heart size and functional exchange capacity together with Doppler wave form assessment of MUA blood flow monthly during gestation.

At calving morphological dimensions of the calf, blood from dam and calf as well as colostrum will be sampled. Milk intake and growth of the calves will be assessed monthly until weaning. Calves will be assessed for age at puberty and measures of reproductive organ development. Bull offspring will be slaughtered at maturity and brain, heart, kidney, muscle and all adipose tissue depots will be taken for subsequent histological, gene expression, epigenetic and protein assessment. Heifer offspring will be mated to investigate effects on in utero protein on development of the second generation of the herd.