TIEMPO DE TRABAJO

2.1.1 Herd treatments for reducing DHA to dairy cows in early lactation

This herd treatment corresponds to Chapter 3. Thirty-six spring-calved cows from the Teagasc Animal and Grassland Research and Innovation Centre (Moorepark, Fermoy, Co. Cork, Ireland) were made available for the study. The cows had a mean calving date of February 9 2015 ± 8.4 d. The 36 cows were assigned to three different herds which

were placed on different DHA for 6 weeks in early lactation from March 9 to April 19 (29-70 days in milk, DIM). The three DHA, expressed as kg dry matter (DM) intake per cow, were 11.8, 14.4 and 15.0, respectively >3.5 cm; these are denoted as low (L- DHA), medium (M-DHA) and high (H-DHA), respectively. The details of the herd management are given in Table 2.1. Paddocks were managed, as described by Kennedy et al. (2007), to ensure the desired DHA for each treatment. The herds were balanced with respect to a number of factors as shown in Table 2.2.

Table 2.1: Experimental and herd management details for DHA experiment.

Period Dates DHA (kg DM) Supplementation Other details

Mean calving date

Feb 9

(1 DIM) 7 - -

Partial

Turnout Feb 9- Feb 22 7

ad-libitum access to grass silage by night + 5 kg concentrates

Following calving, the cows had access to pasture during day and housed during night until February 22

Full turnout Feb 23-Mar 2 13

Concentrates gradually reduced to 0 by March 2 Experimental period in early lactation Mar 9-Apr 19 (29 –70 DIM) 36 cows were assigned to 3 herds on different DHA: 11.8, 14.4 and 15.0 None

Herds grazed within the same paddocks divided with temporary fence. Post experimental period Apr 20-Nov 23 18 None

all 36 cows grazed once more as a single herd

Drying off - - -

Individual cows were dried off when daily milk yield decreased to 8 kg per cow, BCS dropped to 2.5, or when the interval from next calving date was 8 weeks

Table 2.2: Factors on which three herds were balanced.

Period Details SD

Mean calving date Feb 9, 2015 8.4

Breed 16 Holstein Friesian (HF), 13 HF X Jersey, 7 HF X Norwegian Red

Lactation number 2.56 1.42

Bodyweight 523 53.2

Body condition score (BCS)

3.17 0.0142

Pre-experimental daily milk

yield (kg) 25.3 3.70

Milk solids yield (kg) 2.20 0.33

All experimental procedures involving cows were approved by the Teagasc Animal Ethics Committee (TAEC69/2014) and authorised by the Health Products Regulatory Authority (Project licence No.: AE19132/P017), which is the competent authority in Ireland responsible for the implementation of European Union legislation for the protection of animals used for scientific purposes.

2.1.1.1 Milk sampling from DHA experiment

Milk was sampled at 10 day intervals during the period March 9-April 19, 2015 (29-70 DIM), when the herds were on different DHA; this period was denoted early lactation (EL). Thereafter, milk was sampled at 1-3 week intervals for the remainder of the lactation, which was arbitrarily divided into two sub-periods, namely mid lactation (ML, April 27-August31) when cows were 78-183 DIM, and late lactation (LL, September 20-November2) when cows were 205-267 DIM. The number of milk samples in EL, ML and LL were 4, 7 and 4, respectively.

All 36 cows were milked daily at 07:00 and 15:30 and ~250 mL of milk was collected separately from each cow in the evening and morning milkings in sterilised plastic screw cap bottles; evening milk samples in separate 250 mL bottles were held at 4 °C overnight prior to blending with morning milk samples. A composite sample (2 L) for each of the treatment herds was generated by blending the milk samples from

individual cows in the herd, in quantities proportional to the total milk yield of each cow in both evening and morning milkings. The three composite herd milk samples were preserved with sodium azide (0.02 %, w/w) and held at 4 °C until required for further analysis, which was completed within 3-48 h after collection.

2.1.2 Herd treatment for different dairy cow feeding systems

This herd treatment corresponds to Chapters 4, 5, 6 and 8. A separate set of 60 spring- calving dairy cows were allocated to one of the three feeding systems at the Teagasc Animal and Grassland Research and Innovation Centre (Moorepark, Fermoy, Co. Cork, Ireland) both in 2015 and 2016. The feeding systems, imposed from mid-February (1 DIM) to November (300 DIM), were: grazing on perennial ryegrass (Lolium perenne L.) pasture (GRO), grazing on perennial ryegrass and white clover (Trifolium repens L.) pasture (GRC), or housed indoors and offered total mixed ration (TMR). The herds were balanced with respect to a number of factors as shown in Table 2.3, including 2- week pre-experimental milk yield and milk solids yield, as described by McAuliffe et al. (2016). The details of the herd management and feeding systems are given in Table 2.4.

Table 2.3 Factors on which three herds were balanced.

Period Details

Mean calving date Feb 19 (2015 and 2016)

Breed 48 Holstein Friesian + 12 Holstein Friesian × Jersey

Lactation number 12 primiparous + 48 multiparous Economic Breeding Index

(EBI) €185 ± €43

Table 2.4: Experimental and herd management details for DHA experiment.

Period Details

Turnout The cows were placed on the different feeding systems 1 week after calving Sward

Management

GRO and GRC swards were fertilised at 250 kg N/ha/yr. Nitrogen was applied to GRO and GRC swards treatments as urea (46 % N) until the end of April and as calcium ammonium nitrate (27 % N) from early May to mid-September. Grass was allocated to the grazing groups each day to achieve a post grazing sward

pre-grazing herbage mass (>4 cm) and area (m2). Average sward clover content across the year was 23.8 % of herbage dry matter. The target pre-grazing herbage mass was between 1300 and 1600 kg DM/ha above 4 cm.

Stocking rate The grazing treatments were stocked at 2.75 livestock units/Ha in a fully closed farm system.

Grazing rotations Both grazing groups were rotationally grazed, achieving 8.3 grazing rotations in the season.

Grazing cow supplementation

They had a dry matter intake of 18 kg/day per cow. Grazing cows received a mineral supplement in the form of a liquid mineral preparation injected into the water supply (Terra Liquid Minerals, Moone Lodge, Moone, Athy, Co. Kildare, Ireland), giving a mean intake (mg/day per cow) of Na, Mg, Zn, Cu, Se and Co of 5.0, 1.2, 219, 106, 3.8, and 3.0 respectively. The GRO and GRC diets were supplemented with concentrates at a level of 2 kg per cow in November for a period of 25 days, which included the last 2 sampling occasions in 2015 when the cows were 257 and 281 DIM, respectively. During this period, the DMI decreased to 17 kg/day per cow.

TMR cow diet

It consisted of grass silage, maize silage and concentrates, including beet pulp, soybean meal, maize distillers’ grains, rolled barley, rapeseed meal, Megalac®, acidbuf and mineral balancer (O’Callaghan et al., 2016a). The dry matter intake of TMR-fed cows was 7.15 kg grass silage, 7.15 kg maize silage, and 8.3 kg concentrate. The concentrates portion of the TMR feed was supplemented with a commercial mineral balancer, Dairy Hi-Phos (McDonnell Bros. Agricultural Suppliers Ltd, Fermoy, Co. Cork, Ireland) to give added Ca, Na, P, Zn, Cu, Mn, I, Co and Se of 3340, 2000, 1200, 140, 100, 70, 10, 2 and 0.8 mg/kg, respectively. Cows on TMR feeding system were housed in cubicles and fed ad-libitum at 0830 h everyday into individual feed bins which were electronically controlled by Griffith Elder Mealmaster (Griffith Elder and Company Ltd., Suffolk, UK). Drying off Individual cows were maintained on the treatments until the milk yield dropped to

< 8L/d or on November 26 in 2015 and November 29 in 2016.

All experimental procedures involving cows were approved by the Teagasc Animal Ethics Committee and authorised by the Health Products Regulatory Authority (HPRA), which is the competent authority in Ireland responsible for the implementation of European Union legislation (Directive 2010/63/EU) for the protection of animals used for scientific purposes.

2.1.2.1 Milk sampling from different feeding system experiment

Milk from each of the three herds on the GRO, GRC or TMR feeding systems was collected separately in the designated tanks, and denoted as GRO, GRC or TMR milk, respectively. Evening (1530 h) and morning (0730 h) milk from each herd was collected separately in designated refrigerated bulk tanks (5000 L) and milk yields were recorded using DairyMaster milk meters (DairyMaster, Causeway, Co. Kerry, Ireland) en-route

to the bulk tank. Following completion of morning milking, the collected pm and am milks were agitated intermittently for ~ 30 min prior to sampling.

For the study in 2015, ~350 L milk from each herd was collected on 10 separate occasions, at two or three weekly intervals, from June 17 (119 DIM) to November 26 (281 DIM). The milk from each herd was collected in a separate refrigerated bulk tank. A representative 2-L herd milk sample was then withdrawn through the sampling port of each bulk tank into clean 2-L glass bottles and taken immediately to the laboratory for analysis. Milk was analysed for gross composition and elements over the period from June 17 to November 26 (ML: June 17-September 9; LL: September 22- November 26). In the 2016 study, bulk herd milks were collected in ML (May 23-July 20, 94-152 DIM) and LL (September 27-November 5, 221-260 DIM), and evaluated for their Mozzarella cheese- and low-heat skim milk powder (LHSMP) making characteristics.