Cow’s use of feed can now be gauged

Milk comes from cows, no sur­prises there, but how ef­fi­cient are cows at con­vert­ing feed to milk? A Lin­coln Uni­ver­sity stu­dent has de­vel­oped a method to mea­sure how ef­fi­cient the an­i­mals are

South Waikato News - - RURAL DELIVERY -

A goal for all Kiwi dairy farm­ers is the max­imi­sa­tion of milk out­put.

But what is the qual­ity of this milk and how much feed does it take a pint.

Lin­coln Uni­ver­sity doc­toral can­di­date Long (Paul) Cheng of the Fac­ulty of Agri­cul­ture and Life Sci­ences is try­ing to an­swer these ques­tions.

Mr Cheng has de­vel­oped a sim­ple non-in­va­sive method to mea­sure the ef­fi­ciency with which cows con­vert feed pro­tein to milk pro­tein. ‘‘In­ef­fi­cient use of feed pro­tein by cows re­sults in high lev­els of ni­tro­gen in their urine,’’ he said.

‘ ‘ This can lead to in­creased ni­trate leach­ing to ground­wa­ter and el­e­vated lev­els of nitrous ox­ide re­leased to the at­mos­phere.’’ Un­til now, work in this field has been re­stricted by the in­abil­ity to make ac­cu­rate mea­sure­ments of the ef­fi­ciency of in­di­vid­ual an­i­mals.

‘‘So far, my re­sults look promis­ing,’’ Mr Cheng said. ‘‘They have pro­vided strong sup­port for the hy­poth­e­sis that di­etary pro­tein lev­els in­flu­ence the dis­tri­bu­tion of dif­fer­ent forms of ni­tro­gen within the cows’ sys­tems and hence can ul­ti­mately im­pact on ni­trate lev­els in the soil via urine ex­cre­tion.

Mr Cheng’s method is based on the phe­nom­e­non of ni­tro­gen iso­topic frac­tion­a­tion in ru­mi­nants in which two dif­fer­ent, nat­u­rally- present, non-ra­dioac­tive iso­topes of ni­tro­gen ( 14N and 15N) are found ei­ther in the milk (as pro­tein) or the urine (as waste).

‘‘The re­search tech­nique needed to be suit­able for large num­bers of an­i­mals, be­cause it can be used in con­junc­tion with DNA technology to help farm­ers se­lect cows that use their feed more ef­fi­ciently,’’ he said.

Mr Cheng fed the cows in his study di­ets with dif­fer­ent lev­els of pro­tein and col­lected milk, fae­ces and urine and an­a­lysed these for the two iso­topes of ni­tro­gen to mea­sure how ef­fi­ciently the cows used the ni­tro­gen from their di­ets.

His tech­nique will aid re­searchers by pro­vid­ing a sim­ple way to mea­sure ni­tro­gen frac­tion­a­tion in milk.

Ni­tro­gen use ef­fi­ciency can be in­creased in a num­ber of ways, such as by breed­ing im­proved grasses, by the ge­netic se­lec­tion of cows, and by feed­ing an­i­mals more bal­anced di­ets. Mr Cheng’s re­search is part of an in­creas­ingly multi-dis­ci­plinary ap­proach to ad­dress­ing en­vi­ron­men­tal is­sues in ru­mi­nant sys­tems that in­volves re­searchers in plant breed­ing, an­i­mal breed­ing and an­i­mal nutrition.

Re­flect­ing this ap­proach, his PhD su­per­vi­sors in­clude Pro­fes­sor of Dairy Pro­duc­tion Grant Ed­wards and Dr Alastair Ni­col from Lin­coln Uni­ver­sity, and Dr Richard De­whurst from the An­i­mal Bio­science Cen­tre of Tea­gasc, Ire­land.

Pro­fes­sor Ed­wards said the chal­lenge now was ‘‘to un­der­stand the ba­sis of these dif­fer­ences in ni­tro­gen par­ti­tion­ing to elu­ci­date the way in which iso­topes of ni­tro­gen frac­tion­ate in the ru­men and liver’’.

The re­search is funded by the Foun­da­tion for Re­search Sci­ence and Technology’s Dairy Sys­tems for En­vi­ron­men­tal Pro­tec­tion project.

Photo: WAIKATO TIMES FILE

GRASS TO MILK: A Lin­coln Uni­ver­sity doc­toral can­di­date has de­vel­oped a test for how ef­fi­ciently cows turn feed into milk.

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