Finishing cull cows can be a tricky business, with many producers believing that throwing feed at cows is the best way of adding condition quickly.
But new research from Ireland suggests offering cows more than 6kg of concentrate a day on top of grass silage is a wasted effort, with cows offered grass silage and 9kg of concentrates a day failing to deliver improved liveweight gain or carcass weight.
Speaking at this week’s British Society of Animal Science conference, Southport, William Minchin of Teagasc, Moore Park, told delegates replacement rates in Irish dairy herds had risen from 16% in 1990 to 27% in 2003. This meant there were significantly more cull cows to be finished and current Irish data show cull cow carcass weights in Ireland are just 282kg, compared with 343kg in France.
Due to culling patterns there are large numbers of unconditioned dairy cows from the milking herd entering abattoirs in the final third of the year at the end of the cow’s lactation, he explained. “Only 23% of cows killed in 2005 were killed in the first third of the year, with 36% killed in the second third and 41% in the final third.”
To assess the best finishing regime Mr Minchin and colleagues fed cows four different diets, all based on grass silage. The first was grass silage alone, the second grass silage and 3kg of concentrate, the third grass silage and 6kg of concentrate and finally, grass silage and 9kg of concentrate. “Cows were randomly allocated to one of the four diets and concentrates consisted of rolled barley, maize gluten, citrus pulp and dry cow minerals.”
The group fed solely grass silage predictably performed worst, taking an average of 122 days to reach slaughter condition score of 3.5 and gaining just 0.75kg a day. They also had the lightest liveweight at slaughter and carcass cold weight at 699kg and 315kg, respectively.
Meanwhile, the group offered grass silage and 3kg of concentrate achieved a daily gain of 0.91kg a day, took 108 days to reach slaughter and recorded the highest carcass weight at 325kg.
Of the two groups fed higher rates of concentrate, cows fed 6kg a day were the best feed converters, gaining 1.14kg a day and taking 95 days to reach slaughter condition. They recorded an average carcass weight of 322kg.
However, while the group fed 9kg a day achieved slaughter condition quickest at an average of 84 days, they only gained 1.15kg a day, just 0.01kg day more than their 6kg a day fed counterparts. “So, while there are advantages to be found in offering cull cows concentrate feed in the finishing period, there is no gain to be had in feeding more than 6kg a day.
“To achieve optimum value, the finishing criteria used for this trial of 4L fat class at P+ or O conformation must be met, meaning cows intended for further finishing must be carefully selected,” he concluded.