SAC Research

Measurements made at the SAC Dairy Research Centre

Langhill select and control lines of dairy cows are managed as a single group but fed 2 distinct diets.  These diets are expected to reflect the 2 major types of management systems that will exist in the future and are fed as an ad libitum total mixed ration (TMR).  One group is fed a diet consisting of forage that could be home grown (HF) and the other group is fed a diet containing grass silage and around 4 tonnes of concentrate per lactation (HC).  Cows are monitored very extensively for production, health and fertility and feed intake is measured daily during the normal period (365d for HC).  Cows are weighed at every milking (3x daily) and scored for body condition and locomotion weekly.

Consequences of past selection

Selection for production has led to cows that produce more milk but are less fertile.  They also progressively lose body energy over their lifetime.  This has consequences for health and fertility since these are known to be associated with loss of body fat.  Loss of body fat is greatest for cows fed a high forage diet.

Research at SAC has:

• Shown that selection for yield alone has led to a genetic decline in fertility - work by SAC and others in a LINK project has led to the development of a UK fertility index, allowing future selection for both production and good fertility.
• Calculated the correlated reduction in body energy when selection is for yield alone - this knowledge is being used in a new SAC LINK project to identify and characterise Robust Cows with a long term view of producing revised selection indices that improve animal health and welfare.

A new programme of research at the SAC Dairy Research Centre is investigating the matching of genotypes to systems - when selection indices are too narrow, cows may not be best suited to any management system.  The consequences of a genotype environment mismatch can be identified before it becomes a national problem through the propagation of inappropriate genotypes.