Milk Synthesis and Dairy Herd Management

Milk synthesis

Milk synthesis • Proteins – major groups are caseins and whey proteins • Lactose – unique to mammary gland • Fat – droplets enveloped by membrane • Ruminants – fatty acids synthesized from volatile fatty acids (acetate)

Milk ejection • Milk “letdown” • Neuroendocrine reflex • Milk not removed solely by suckling action • Passive removal possible from gland cistern • Controlled by myoepithelial cells • Oxytocin stored in posterior pituitary gland • Action within 30 – 60 seconds

Milking Equipment • Pulsation system alternately… • Introduces atmospheric air into hoses and teat cup chamber • Removes air from system • Pulsation rate = # of cycles of alternating negative and atmospheric pressure; ~ 50 cycles/minute

Milk ejection II • New milk synthesis inhibited after ~ 18 h of milk non-removal • Complementary or residual milk (10- 20% of total) • Inhibition • Stress, emotional upset • Administration of exogenous oxytocin

Involution • 45 – 60 d in dairy cows • “Regression” & “remodeling” in the mammary gland • Decreased metabolic activity • Altered size, shape, # of alveoli • Length of dry period influences subsequent lactational performance

Decreasing milk production • Lack of milk removal • Pressure builds up in gland • FIL: chemical signal in milk to cells? • After 16-18 h, milk synthesis decreases • Important to avoid in early lactation • Mastitis leading to development of scar tissue

Bovine Somatotropin • Increase milk yield ~ 10 lb per cow • Increases nutrient utilization by the mammary gland • Milk yield • increases gradually during rbST supplementation, up to max ~ d 6 • Administration after peak milk yield • Increased costs: labor, rbST, DMI • Increase in DMI lags behind MY

Milking 4x or 6x • Milking frequency: ~ 8 lb per cow • Early in lactation: increased peak and persistency • Milk fresh cows first and last at each milking for first 21 d • Increased labor, use of milking equipment, feed costs -- 0.5 lb DM for 1 lb milk

Photoperiod--Lactation • 16 to 18 h light per day increases MY 5 to 15% • Low investment, size neutral • Barns are traditionally dimly lit • Estimate # of fixtures needed to increase lighting • Cleaning required

Photoperiod – Dry Period • Cows on 8 h vs 16 h during dry period produced ~ 7 lb/d more milk during early part of subsequent lactation

Cow health issues – transition period • Milk fever (parturient paresis) • Ketosis • Retained placenta

Displaced Abomasum Normal DA Right Left

Mastitis • Infectious disease • Inflammation of secretory tissue

Classification • Clinical • Shorter duration • Causes visible changes in udder and milk • Acute cases – become systemic infections • Subclinical • Longer duration • Majority of mastitis cases • May be chronic

Detection of mastitis • Appearance of milk • Somatic Cell Count • Leukocytes & epithelial (secretory) cells • leukocytes • secretory cells • California Mastitis Test (CMT) – detects DNA in milk • Bacteriologic testing

Milk Synthesis and Dairy Herd Management