In many of the above ‘trade-off’ situations, either luteinising hormone (LH) pulse or surge patterns (or both) in dairy cows are disrupted leading to reduced fertility (feeding: Butler, 2003; environmental temperature: Badinga et al., 1994; mastitis: Hockett et al., 2005; lameness: review: Dobson et al., 2008). This evidence concerns the gene PLOD1 and mastitis.