ROLES OF MATERNAL VISION AND OLFACTION IN SUCKLING-MEDIATED INHIBITION OF LUTEINIZING-HORMONE SECRETION, EXPRESSION OF MATERNAL SELECTIVITY, AND LACTATIONAL PERFORMANCE OF BEEF-COWS

The roles of maternal vision and olfaction in regulating the suckling- mediated inhibition of LH secretion, expression of maternal selectivit y and lactational performance was examined in anestrous beef cows (n = 57). Pluriparous cows were allotted randomly to one of 10 groups betw een 17 and 21 days postcalving (Experimental Day 0). Groups 1-8 includ ed cows that were either intact, blind, anosmic, or blind and anosmic, and were control-suckled by either their own or unrelated (''alien'') calves every 6 h for 6 days. Groups 9 and 10 served as positive contr ols and were left intact and weaned, or were anosmic, blind, and weane d. The frequency of LH pulses (pulses/5 h) remained unchanged over the 6-day experiment in sighted and olfactory-intact groups suckling thei r own calves (1.2 +/- 0.01). In contrast, cows that were olfactory-int act or sighted and suckling alien calves, blind and anosmic and suckli ng their own or alien calves, or weaned exhibited prompt increases (p < 0.001) in LH pulse frequency to a maximum of 4.6 +/- 0.3 pulses/5 h within 6 days. Mean frequency was greater in these groups (p < 0.05) t han in olfactory-intact or sighted groups suckling their own carves. E nforced suckling by an alien calf attenuated (p < 0.001) milk producti on and calf weight gain, and a greater ip < 0.05) proportion of cows p resented with aliens during behavioral tests physically rejected suckl ing compared to those presented with their own calves. These results c onfirm that suckling-related events sustain the inhibited pattern of L H secretion in cows only if the offspring are positively identified as their own. Olfaction and vision are equally effective in permitting c alf identification, but elimination of both senses prevents calf ident ification and the negative effects of suckling on LH secretion.