Protein push

Led by Goondiwindi's Dr Viv Perry and PHD student Katrina Copping, the project involved 360 yearling heifers, making it one of the largest research programs of its kind in the world. The project was funded by an industry collaborative grant from the Australian Research Council (ARC) in collaboration with S Kidman & Co and Ridley Agriproducts.

Dr Perry said the research findings had direct benefits for stud and commercial cattle producers."The aim of the research was to look at the economic value of supplementing heifers and when it is most beneficial to supplement with protein," she said.

"We had done previous research with 120 AACo heifers calving at three years old in Goondiwindi that had looked at first and second trimester protein intake and we found that the second trimester was really important for altering birth weights and that the first trimester was vital in terms of organ and muscle development.

"I wanted to do a large-scale research project that looked at what effect there was in the 60 days prior to conception and the 90 days after, in heifers calving at two years old. We are killing most steers between 18 and 20 months of age, which means they are spending 30 to 40 percent of their life in the womb, so we really wanted to know what was influencing their development during this time so we could optimise it."

The research involved 360 Santa Gertrudis heifers that were sourced from S Kidman & Co properties in the Birdsville district and trucked to a purpose-built feedlot in Sedan, South Australia, in November 2011.

The heifers were all of a similar weight and age and pregnancy tested empty. They were blooded for BVD status and vaccinated for the common communicable diseases prior to trucking.

After being trucked to Sedan, the heifers were handled with low-stress stock handling techniques and trained to eat in their individual stalls.

The heifers were individually fed diets at 14pc crude protein (CP) or low 7pc CP for 60 days before conception by AI and 23 days post conception and from 23 days to the end of the first trimester.

Pregnancy was confirmed by rectal ultrasound at 36 days post-conception. The overall pregnancy rate was 35.3pc.

Blood flows to the foetus and foetal development were monitored during pregnancy.

Fifty of the heifers were killed at 90 days pregnant and the foetuses and placentas were assessed in laboratories in Australia and the UK to analyse organ growth and development. The rest of the heifers went on to calve out and these progeny were measured to adulthood.

The males were used in a NFI trial at the University of New England prior to slaughter at the John Dee abattoir at Warwick in August this year.

Comprehensive carcase data according to standard Aus-Meat procedures were collected at the kill floor and in the chiller. Tissue samples from these carcases are still being assessed in the UK and Australia. The female progeny were trucked to Bonyi, Goondiwindi, and have been joined in order for research to continue on the second generation.

Dr Perry said one of the most significant commercial findings of her research so far was the higher incidence of early embryonic loss in the heifers fed a low-protein diet.

"Heifers that received the high-protein diet during the peri-conception period had significantly higher circulation progesterone levels at 23 and 36dpc (days post conception by AI) compared to those that received the low protein diet.

"A reduction in progesterone at the levels recorded has been associated with increased levels of embryonic loss.

"By using 7ng/ml of progesterone in plasma as indicative of pregnancy, we observed that 27 heifers lost the embryo between 23dpc and 36dpc and 19 (70pc) of these had received low protein peri-conception. Supplementation therefore may increase pregnancy rates by 15pc.

"To me that's a really good take-home message for producers - make sure your heifers have good levels of protein when they are in with the bull. If you do that you will decrease your chances of losing calves in that very early stage."

Dr Perry said the results of the chiller assessments on the male progeny were also enlightening. There were no significant differences in P8 fat depth as the result of maternal nutritional treatment, live weight prior to slaughter, dressing percentage or hot standard carcase weight.

However, EMA was significantly greater (5cm) in those animals whose dam received a high-protein diet during the first trimester, both with and without adjustment for carcase weight.

"Maternal nutrition affects foetal development, especially skeletal muscle development. The early foetal stage is crucial for skeletal muscle development because there are no net increase in muscle fibre numbers after birth.

"Therefore, any decrease in the number of muscle fibres during foetal life permanently reduces muscle mass.

"In cattle, primary muscle fibres form within the first two months of conception with the majority of secondary muscle fibres forming between two and eight months gestation," she said.

“The positive effect of higher protein on increased EMA in progeny at slaughter demonstrates the potential to alter carcase composition by nutritional management of heifers during pregnancy.”

The research also revealed some enlightening results around post-natal development of bulls.

The male progeny were assessed from 11 to 18 months of age for scrotal circumference (SC), sperm motility (mass activity and percent progressively motile sperm) as well as the per cent of morphologically normal sperm.

It was found that at 12 months of age, mass activity and motility were both higher (0.05pc) and percent normal sperm (PNS) also tended to be higher in ejaculates obtained from calves born to dams that received the high peri-conception diet compared to the calves whose dams received the low- protein peri-conception diet.

After puberty, the effects of the peri-conception diet upon sperm quality were reduced although the PNS still tended to be higher in ejaculates from those bulls whose dams received the high-protein peri-conception diet.

“These effects upon the earlier development of commercially important reproductive traits may have relevance to the stud industry where quality sperm of production is assessed prior to sale.

“As these breeding soundness examinations are often done three months prior to sale, at 15 months of age, it could be suggested that protein supplementation during early pregnancy would be commercially beneficial.

“From a stud producers’ point of view I would suggest that it is really important that in the early part of pregnancy, their heifers in particular have good nutrition because it can really affect the developing testis in their male calves.”

In studs aiming to produce yearling bulls this may also be particularly relevant.

Dr Perry is now keen to continue her research on the tissues collected and on the second generation of cattle at Goondiwindi.

She divides her time between the UK, where she has a position at the University of Nottingham Veterinary School, and the Queensland research.

Her husband, Ray Cranney, initially made the move with her but will now split his time between the UK and their Goondiwindi property.

“I have been in the UK for three years now,” she said.

She is currently working on a heifer research project in the UK as well as completing work on bull fertility in Queensland.