Sizing up heifers

Skeletal measurements such as length and pelvic area have been added to an updated growth chart to determine optimum size for Holstein heifers. And these measurements should be used, says a University of Wisconsin researcher, because they are often more pertinent to lactation performance and health and weight gain.

Body condition score, too, is included, because so many data link dystocia to heifer condition at calving.

The chart shown comes from Pat Hoffman. He calls it "Body size criteria for the current U.S. Holstein genotype." It's meant to provide commercial producers a reference to evaluate replacement heifer management—under ideal conditions.

Replacement-heifer growth recommendations are commonly based on single body-weight or wither- height criterion at the corresponding age, says Hoffman. These recommendations are useful, but do not incorporate genetic differences of body size.

In his chart, optimal average body weight before calving is 1,366 lb. The Marshfield, Wis., dairy scientist explains that the figure is representative of the prepartum weight observed in recent studies on calving age, and is close to the mid-point of the body-weight range (1,300 to 1,400 lb.) shown to optimize first-lactation milk yield. The 1,366-lb. target also falls close to the average weight of Holstein heifers in high-producing Wisconsin herds in a 1992 study. Wither-height criteria are based on Penn State calculations.

As the chart shows, the influence of genetics on prepartum body weight (upper and lower range) is about 100 lb., Hoffman notes. Calf birth weight was set at 93 lb. and weaning was assumed to occur at two months of age at 185 lb.

A comment about average daily gain: A gain of 1.75 lb./day has not proven detrimental to milk yield or mammary development, adds Hoffman.

Although it has been suggested that heifers gaining over 1.75 lb./day are predisposed to laminitis and sole hemorrhages, he also discounts that concern. "The modern Holstein heifer fed all baled hay has the potential to gain 1.75 lb., provided she's in a quality environment," he points out. "A diet of all long-stem forage would not likely result in laminitis. While laminitis is a concern, cause should be expressed in diet energy content or lack of dietary fiber and not correlated to growth rate."

It has also been theorized that NRC protein requirements are insufficient for heifers and limit stature growth, continues Hoffman. "It's true that protein must be adequate to optimize growth and frame development," he says, "but it has been demonstrated that oversupplying protein will not further enhance growth or frame." He adds that recent research on protein nutrition has not clearly defined strategies to consistently improve growth or frame development.

To work, replacement monitoring programs should be simple and minimize labor, says the Wisconsin heifer expert. Hoffman suggests two systems:

• Breeding/calving. Birth dates of replacement heifers are recorded, heifers are identified. Heifers are measured (heart girth, wither height, body condition scored) at breeding and 14 days before calving. Growth rate, age/weight relationships can be calculated.

• Single time measurement: All replacements on the farm are measured (heart girth, wither height, body scored) on the same day. Data are plotted and compared to objectives.

Body-size criteria

	Upper range					Lower range
Age, mo.	| BW	ADG	WH	BL	BCS |	| BW	ADG	WH	BL	BCS |
0	93	...	30	32	...	93	...	30	32	...
1	139	1.5	32	34	...	139	1.5	32	34	...
2	185	1.5	34	37	...	185	1.5	34	37	...
3	242	1.8	36	39	2.2	236	1.7	36	39	2.2
4	298	1.8	39	41	...	287	1.7	38	41	...
5	355	1.8	40	43	...	339	1.7	40	43	...
6	410	1.8	41	46	2.3	390	1.7	41	45	2.3
7	467	1.8	43	48	...	441	1.7	42	47	...
8	522	1.8	44	50	...	491	1.7	43	48	...
9	580	1.8	44	52	2.4	544	1.7	44	50	2.4
10	635	1.8	46	53	...	595	1.7	45	52	...
11	692	1.8	46	55	...	646	1.7	46	54	...
12	747	1.8	47	56	2.8	696	1.7	46	55	2.8
13	804	1.8	48	58	...	749	1.7	47	56	...
14	860	1.8	49	59	...	800	1.7	48	58	...
15	917	1.8	50	61	3.0	851	1.7	49	59	3.0
16	972	1.8	50	62	...	901	1.7	50	60	...
17	1,029	1.8	51	63	...	952	1.7	50	61	...
18	1,084	1.8	52	64	3.2	1,005	1.7	51	62	3.2
19	1,142	1.8	52	65	...	1,056	1.7	52	63	...
20	1,197	1.8	53	65	...	1,106	1.7	52	64	...
21	1,254	1.8	54	66	3.4	1,157	1.7	53	65	3.4
22	1,309	1.8	54	67	...	1,210	1.7	53	66	...
23	1,366	1.8	55	67	...	1,261	1.7	54	66	...
24	1,422	1.8	56	68	3.5	1,311	1.7	54	67	3.5
7-d postpartum	1,281					1,181
30-d postpartum	1,192					1,102

WH=wither height, BL=body length from the point of shoulder to the back of the pelvis, BCS=body condition score.
Pelvic area > 260 sq.cm